diff --git a/src/alerts.ts b/src/alerts.ts
new file mode 100644
index 00000000..f05a8134
--- /dev/null
+++ b/src/alerts.ts
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { IToastProps } from '@blueprintjs/core';
+import alerts from './alerts/alerts';
+import explorer from './explorer/alerts';
+import { CreateToast } from './i18nToaster';
+
+/** This collects alerts from all of the subsystems of the app */
+const alertDomains = {
+    alerts,
+    explorer,
+};
+
+/** Gets the type of available alert domains. */
+export type AlertDomain = keyof typeof alertDomains;
+
+/**
+ * Gets the type of available specific alerts for a domain.
+ * @template D The domain.
+ */
+export type AlertSpecific<D extends AlertDomain> = keyof typeof alertDomains[D];
+
+/**
+ * Gets the instance type of the object in the lookup table.
+ * @template D The domain.
+ * @template S The specific instance name in the domain.
+ */
+type AlertInstance<
+    D extends AlertDomain,
+    S extends AlertSpecific<D>,
+> = typeof alertDomains[D][S] extends CreateToast<infer P, infer A>
+    ? CreateToast<P, A>
+    : never;
+
+/**
+ * Gets the type of the `onAlert` callback for a specific instance in the lookup table.
+ * @template D The domain.
+ * @template S The specific instance name in the domain.
+ */
+export type AlertCallback<
+    D extends AlertDomain,
+    S extends AlertSpecific<D>,
+> = Parameters<AlertInstance<D, S>>[0];
+
+/**
+ * Gets the type of available actions for a specific instance in the lookup table.
+ * @template D The domain.
+ * @template S The specific instance name in the domain.
+ */
+export type AlertActions<D extends AlertDomain, S extends AlertSpecific<D>> =
+    | Parameters<Parameters<AlertInstance<D, S>>[0]>[0];
+
+/**
+ * Gets the type of the properties for a specific instance in the lookup table.
+ * @template D The domain.
+ * @template S The specific instance name in the domain.
+ */
+export type AlertProps<D extends AlertDomain, S extends AlertSpecific<D>> = Parameters<
+    AlertInstance<D, S>
+>[1];
+
+/**
+ * Gets the alert creation function from the lookup table and uses it to create
+ * a new alert (toast).
+ *
+ * @param domain The alert domain (app subsystem).
+ * @param specific The specific alert for the domain.
+ * @param onAlert The callback that will be called when the alert is dismissed.
+ * @param props Any additional properties required by this specific alert.
+ * @returns The newly created alert properties.
+ */
+export function getAlertProps<D extends AlertDomain, S extends AlertSpecific<D>>(
+    domain: D,
+    specific: S,
+    onAlert: AlertCallback<D, S>,
+    props: AlertProps<D, S>,
+): IToastProps {
+    const create = alertDomains[domain][specific] as unknown as CreateToast<
+        Record<string, unknown> | never,
+        string
+    >;
+    return create(onAlert, props);
+}
diff --git a/src/notifications/UnexpectedErrorNotification.scss b/src/alerts/UnexpectedErrorAlert.scss
similarity index 86%
rename from src/notifications/UnexpectedErrorNotification.scss
rename to src/alerts/UnexpectedErrorAlert.scss
index 286a790d..b7302997 100644
--- a/src/notifications/UnexpectedErrorNotification.scss
+++ b/src/alerts/UnexpectedErrorAlert.scss
@@ -3,7 +3,7 @@
 
 @use '@blueprintjs/core/lib/scss/variables' as bp;
 
-pre.pb-notification-stack-trace {
+pre.pb-alerts-stack-trace {
     max-width: bp.$pt-grid-size * 50;
     max-height: bp.$pt-grid-size * 50;
     overflow: auto;
diff --git a/src/notifications/UnexpectedErrorNotification.tsx b/src/alerts/UnexpectedErrorAlert.tsx
similarity index 68%
rename from src/notifications/UnexpectedErrorNotification.tsx
rename to src/alerts/UnexpectedErrorAlert.tsx
index 7880d929..f1938484 100644
--- a/src/notifications/UnexpectedErrorNotification.tsx
+++ b/src/alerts/UnexpectedErrorAlert.tsx
@@ -1,23 +1,21 @@
 // SPDX-License-Identifier: MIT
-// Copyright (c) 2021-2022 The Pybricks Authors
+// Copyright (c) 2022 The Pybricks Authors
 
-// Provides special notification contents for unexpected errors.
-
-import './UnexpectedErrorNotification.scss';
+import './UnexpectedErrorAlert.scss';
 import { AnchorButton, Button, ButtonGroup, Collapse, Intent } from '@blueprintjs/core';
 import { useI18n } from '@shopify/react-i18n';
 import React, { useState } from 'react';
 import { useId } from 'react-aria';
+import { CreateToast } from '../i18nToaster';
 import { I18nId } from './i18n';
 
-type UnexpectedErrorNotificationProps = {
-    messageId: I18nId;
-    err: Error;
+type UnexpectedErrorAlertProps = {
+    error: Error;
 };
 
-const UnexpectedErrorNotification: React.VoidFunctionComponent<
-    UnexpectedErrorNotificationProps
-> = ({ messageId, err }) => {
+const UnexpectedErrorAlert: React.VoidFunctionComponent<UnexpectedErrorAlertProps> = ({
+    error,
+}) => {
     // istanbul ignore next: babel-loader rewrites this line
     const [i18n] = useI18n();
     const [isExpanded, setIsExpanded] = useState(false);
@@ -25,7 +23,7 @@ const UnexpectedErrorNotification: React.VoidFunctionComponent<
 
     return (
         <>
-            <p>{i18n.translate(messageId, { errorMessage: err.message })}</p>
+            <p>{i18n.translate(I18nId.Message, { errorMessage: error.message })}</p>
             <span>
                 <Button
                     aria-labelledby={labelId}
@@ -37,7 +35,7 @@ const UnexpectedErrorNotification: React.VoidFunctionComponent<
                 <span id={labelId}>{i18n.translate(I18nId.TechnicalInfo)}</span>
             </span>
             <Collapse isOpen={isExpanded}>
-                <pre className="pb-notification-stack-trace">{err.stack}</pre>
+                <pre className="pb-alerts-stack-trace">{error.stack}</pre>
             </Collapse>
             <div>
                 <ButtonGroup minimal={true} fill={true}>
@@ -46,7 +44,7 @@ const UnexpectedErrorNotification: React.VoidFunctionComponent<
                         icon="duplicate"
                         onClick={() =>
                             navigator.clipboard.writeText(
-                                `\`\`\`\n${err.stack || err.message}\n\`\`\``,
+                                `\`\`\`\n${error.stack || error.message}\n\`\`\``,
                             )
                         }
                     >
@@ -57,7 +55,7 @@ const UnexpectedErrorNotification: React.VoidFunctionComponent<
                         icon="virus"
                         href={`https://github.com/pybricks/support/issues?q=${encodeURIComponent(
                             'is:issue',
-                        )}+${encodeURIComponent(err.message)}`}
+                        )}+${encodeURIComponent(error.message)}`}
                         target="_blank"
                     >
                         {i18n.translate(I18nId.ReportBug)}
@@ -68,4 +66,11 @@ const UnexpectedErrorNotification: React.VoidFunctionComponent<
     );
 };
 
-export default UnexpectedErrorNotification;
+export const unexpectedError: CreateToast<{ error: Error }> = (onAction, { error }) => {
+    return {
+        message: <UnexpectedErrorAlert error={error} />,
+        icon: 'error',
+        intent: Intent.DANGER,
+        onDismiss: () => onAction('dismiss'),
+    };
+};
diff --git a/src/alerts/actions.ts b/src/alerts/actions.ts
new file mode 100644
index 00000000..70c630fb
--- /dev/null
+++ b/src/alerts/actions.ts
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { createAction } from '../actions';
+import { AlertActions, AlertDomain, AlertProps, AlertSpecific } from '../alerts';
+
+/**
+ * Action that requests to show an alert to the user.
+ *
+ * @param domain The alert domain (app subsystem).
+ * @param specific The specific alert for the domain.
+ * @param props Any additional properties required by this specific alert.
+ */
+export const alertsShowAlert = createAction(
+    <D extends AlertDomain, S extends AlertSpecific<D>>(
+        domain: D,
+        specific: S,
+        props: AlertProps<D, S>,
+    ) => ({
+        type: 'alerts.action.showAlert',
+        domain,
+        specific,
+        props,
+    }),
+);
+
+/**
+ * Action that indicates the alert requested by {@link alertsShowAlert} was
+ * dismissed.
+ *
+ * @param domain The alert domain (app subsystem).
+ * @param specific The specific alert for the domain.
+ * @param action The user-selected action that dismissed the alert.
+ */
+export const alertsDidShowAlert = createAction(
+    <D extends AlertDomain, S extends AlertSpecific<D>>(
+        domain: D,
+        specific: S,
+        action: AlertActions<D, S>,
+    ) => ({
+        type: 'alerts.action.didShowAlert',
+        domain,
+        specific,
+        action,
+    }),
+);
diff --git a/src/alerts/alerts.ts b/src/alerts/alerts.ts
new file mode 100644
index 00000000..286b045d
--- /dev/null
+++ b/src/alerts/alerts.ts
@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { unexpectedError } from './UnexpectedErrorAlert';
+
+// gathers all of the alert creation functions for passing up to the top level
+export default { unexpectedError };
diff --git a/src/alerts/i18n.test.ts b/src/alerts/i18n.test.ts
new file mode 100644
index 00000000..d0ceda4a
--- /dev/null
+++ b/src/alerts/i18n.test.ts
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2020-2022 The Pybricks Authors
+
+import { lookup } from '../../test';
+import { I18nId } from './i18n';
+import en from './translations/en.json';
+
+describe('Ensure .json file has matches for I18nId', () => {
+    test.each(Object.values(I18nId))('%s', (id) => {
+        expect(lookup(en, id)).toBeDefined();
+    });
+});
diff --git a/src/alerts/i18n.ts b/src/alerts/i18n.ts
new file mode 100644
index 00000000..f6d2a72e
--- /dev/null
+++ b/src/alerts/i18n.ts
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2020-2022 The Pybricks Authors
+
+export enum I18nId {
+    Message = 'message',
+    TechnicalInfo = 'technicalInfo',
+    CopyErrorMessage = 'copyErrorMessage',
+    ReportBug = 'reportBug',
+}
diff --git a/src/alerts/sagas.test.ts b/src/alerts/sagas.test.ts
new file mode 100644
index 00000000..07c582e1
--- /dev/null
+++ b/src/alerts/sagas.test.ts
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { IToastOptions, IToastProps, IToaster } from '@blueprintjs/core';
+import { waitFor } from '@testing-library/dom';
+import { AsyncSaga } from '../../test';
+import { alertsDidShowAlert, alertsShowAlert } from './actions';
+import alerts from './sagas';
+
+afterEach(() => {
+    jest.clearAllMocks();
+});
+
+class TestToaster implements IToaster {
+    private toasts = new Array<IToastOptions>();
+
+    public getToasts(): IToastOptions[] {
+        return this.toasts;
+    }
+
+    public show(props: IToastProps, key?: string): string {
+        if (!key) {
+            throw new Error('key is required!');
+        }
+
+        this.toasts.push({ key, ...props });
+
+        return key;
+    }
+
+    public dismiss(key: string): void {
+        const index = this.toasts.findIndex((t) => t.key === key);
+
+        if (index < 0) {
+            return;
+        }
+
+        const toast = this.toasts.at(index);
+        toast?.onDismiss?.(false);
+
+        this.toasts.splice(index, 1);
+    }
+
+    public clear(): void {
+        throw new Error('this method should never be called!');
+    }
+}
+
+describe('handleShowAlert', () => {
+    let toaster: TestToaster;
+    let saga: AsyncSaga;
+
+    beforeEach(async () => {
+        toaster = new TestToaster();
+        jest.spyOn(toaster, 'show');
+        jest.spyOn(toaster, 'dismiss');
+        saga = new AsyncSaga(alerts, { toaster });
+    });
+
+    it('should show toast', async () => {
+        saga.put(
+            alertsShowAlert('alerts', 'unexpectedError', {
+                error: { name: 'TestError', message: 'test error' },
+            }),
+        );
+
+        expect(toaster.dismiss).not.toHaveBeenCalled();
+        expect(toaster.show).toHaveBeenCalled();
+
+        toaster.dismiss(toaster.getToasts().at(-1)?.key ?? '');
+
+        await expect(saga.take()).resolves.toEqual(
+            alertsDidShowAlert('alerts', 'unexpectedError', 'dismiss'),
+        );
+    });
+
+    it('should show close and re-open toast with same key', async () => {
+        // request to show the same alert twice
+        saga.put(
+            alertsShowAlert('alerts', 'unexpectedError', {
+                error: { name: 'TestError', message: 'test error' },
+            }),
+        );
+        saga.put(
+            alertsShowAlert('alerts', 'unexpectedError', {
+                error: { name: 'TestError', message: 'test error' },
+            }),
+        );
+
+        // at this point, show has only been called once to display the first alert
+        expect(toaster.show).toHaveBeenCalled();
+        // and then dismiss was called to close it
+        expect(toaster.dismiss).toHaveBeenCalled();
+
+        // which should result in an action
+        await expect(saga.take()).resolves.toEqual(
+            alertsDidShowAlert('alerts', 'unexpectedError', 'dismiss'),
+        );
+
+        // then after a delay, the second alert is shown
+        await waitFor(() => expect(toaster.show).toHaveBeenCalledTimes(2));
+
+        // then we dismiss it manually, like normal
+        toaster.dismiss(toaster.getToasts().at(-1)?.key ?? '');
+
+        // and get the action for the second dismiss
+        await expect(saga.take()).resolves.toEqual(
+            alertsDidShowAlert('alerts', 'unexpectedError', 'dismiss'),
+        );
+    });
+
+    afterEach(async () => {
+        await saga.end();
+    });
+});
diff --git a/src/alerts/sagas.ts b/src/alerts/sagas.ts
new file mode 100644
index 00000000..f6421dc0
--- /dev/null
+++ b/src/alerts/sagas.ts
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { IToaster } from '@blueprintjs/core';
+import { eventChannel } from 'redux-saga';
+import { delay, getContext, put, take, takeEvery } from 'typed-redux-saga/macro';
+import { getAlertProps } from '../alerts';
+import { alertsDidShowAlert, alertsShowAlert } from './actions';
+
+export type AlertsSagaContext = { toaster: IToaster };
+
+/** Shows an alert to the user and avoids duplicate alerts. */
+function* handleShowAlert(action: ReturnType<typeof alertsShowAlert>): Generator {
+    const toaster = yield* getContext<IToaster>('toaster');
+
+    const key = `${action.domain}.${action.specific}.${JSON.stringify(action.props)}`;
+
+    const existing = toaster.getToasts().filter((t) => t.key === key);
+
+    // if a toast with the same parameters is already open, close it so we
+    // can open it again without duplicates.
+    if (existing.length > 0) {
+        toaster.dismiss(key);
+        yield* delay(500);
+    }
+
+    const chan = eventChannel<string>((emit) => {
+        const props = getAlertProps(action.domain, action.specific, emit, action.props);
+        toaster.show(props, key);
+
+        // have to return an unsubscribe function to not break things
+        return () => undefined;
+    });
+
+    try {
+        const alertAction = yield* take(chan);
+
+        yield* put(alertsDidShowAlert(action.domain, action.specific, alertAction));
+    } finally {
+        chan.close();
+    }
+}
+
+export default function* (): Generator {
+    yield* takeEvery(alertsShowAlert, handleShowAlert);
+}
diff --git a/src/alerts/translations/en.json b/src/alerts/translations/en.json
new file mode 100644
index 00000000..b348134d
--- /dev/null
+++ b/src/alerts/translations/en.json
@@ -0,0 +1,6 @@
+{
+    "message": "An unexpected error occurred. Please consider reporting this so we can make a better error message.",
+    "technicalInfo": "Expand for detailed technical information",
+    "copyErrorMessage": "Copy Error Message",
+    "reportBug": "Report Bug"
+}
diff --git a/src/editor/error.ts b/src/editor/error.ts
new file mode 100644
index 00000000..e420ee0f
--- /dev/null
+++ b/src/editor/error.ts
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { CustomError } from '../utils/customError';
+
+/** Specific errors for editor subsystem. */
+export type EditorErrorName = 'FileInUse';
+
+/** Error class for editor subsystem. */
+export class EditorError extends CustomError<EditorErrorName> {}
diff --git a/src/editor/sagas.test.ts b/src/editor/sagas.test.ts
index a350790e..6a50edd9 100644
--- a/src/editor/sagas.test.ts
+++ b/src/editor/sagas.test.ts
@@ -10,6 +10,7 @@ import {
     fileStorageDidReadFile,
     fileStorageReadFile,
 } from '../fileStorage/actions';
+import { acquireLock } from '../utils';
 import {
     editorActivateFile,
     editorCloseFile,
@@ -21,6 +22,7 @@ import {
     editorDidOpenFile,
     editorOpenFile,
 } from './actions';
+import { EditorError, EditorErrorName } from './error';
 import { ActiveFileHistoryManager, OpenFileInfo, OpenFileManager } from './lib';
 import editor from './sagas';
 
@@ -51,6 +53,22 @@ it('should activate files from storage', async () => {
     await saga.end();
 });
 
+/**
+ * Asymmetric matcher for matching errors by name while ignoring the message.
+ * @param name The name to match.
+ * @returns An asymmetric matcher cast to an EditorError so that it can be
+ * passed to action functions.
+ */
+function expectEditorError(name: EditorErrorName): EditorError {
+    const matcher: jest.AsymmetricMatcher & Record<string, unknown> = {
+        $$typeof: Symbol.for('jest.asymmetricMatcher'),
+        asymmetricMatch: (other) => other instanceof EditorError && other.name === name,
+        toAsymmetricMatcher: () => `[EditorError: ${name}]`,
+    };
+
+    return matcher as unknown as EditorError;
+}
+
 describe('per-editor sagas', () => {
     let saga: AsyncSaga;
     let monacoEditor: monaco.editor.IStandaloneCodeEditor;
@@ -70,70 +88,92 @@ describe('per-editor sagas', () => {
     });
 
     describe('handleEditorOpenFile', () => {
-        beforeEach(async () => {
-            jest.spyOn(OpenFileManager.prototype, 'add');
-            jest.spyOn(OpenFileManager.prototype, 'remove');
-            saga.put(editorOpenFile('test.file'));
-
-            await expect(saga.take()).resolves.toEqual(
-                fileStorageReadFile('test.file'),
+        it('should fail if file is already in use', async () => {
+            const releaseLock = await acquireLock(
+                'pybricks.editor+pybricksCode:test.file',
             );
+            expect(releaseLock).toBeDefined();
+
+            try {
+                saga.put(editorOpenFile('test.file'));
+
+                await expect(saga.take()).resolves.toEqual(
+                    editorDidFailToOpenFile(
+                        'test.file',
+                        expectEditorError('FileInUse'),
+                    ),
+                );
+            } finally {
+                await releaseLock?.();
+            }
         });
 
-        it('should propagate error from fileStorageReadFile', async () => {
-            const testError = new Error('test error');
-
-            saga.put(fileStorageDidFailToReadFile('test.file', testError));
-
-            await expect(saga.take()).resolves.toEqual(
-                editorDidFailToOpenFile('test.file', testError),
-            );
-
-            expect(OpenFileManager.prototype.add).not.toHaveBeenCalled();
-        });
-
-        describe('read succeeded', () => {
-            let model: monaco.editor.ITextModel;
-
+        describe('not already in use', () => {
             beforeEach(async () => {
-                monaco.editor.onDidCreateModel((m) => (model = m));
-
-                saga.put(fileStorageDidReadFile('test.file', ''));
-
-                expect(model).toBeDefined();
+                jest.spyOn(OpenFileManager.prototype, 'add');
+                jest.spyOn(OpenFileManager.prototype, 'remove');
+                saga.put(editorOpenFile('test.file'));
 
                 await expect(saga.take()).resolves.toEqual(
-                    editorDidOpenFile('test.file'),
+                    fileStorageReadFile('test.file'),
                 );
-
-                expect(OpenFileManager.prototype.add).toHaveBeenCalled();
-                expect(OpenFileManager.prototype.remove).not.toHaveBeenCalled();
             });
 
-            it('should close file if task is canceled', async () => {
-                jest.spyOn(model, 'dispose');
+            it('should propagate error from fileStorageReadFile', async () => {
+                const testError = new Error('test error');
 
-                saga.cancel();
-
-                // model should be disposed before fileStorageClose
-                expect(model.dispose).toHaveBeenCalled();
-                expect(OpenFileManager.prototype.remove).toHaveBeenCalled();
-
-                // editorDidCloseFile is not called since we did not put editorCloseFile
-            });
-
-            it('should close when requested', async () => {
-                jest.spyOn(model, 'dispose');
-
-                saga.put(editorCloseFile('test.file'));
-
-                // model should be disposed before fileStorageClose
-                expect(model.dispose).toHaveBeenCalled();
-                expect(OpenFileManager.prototype.remove).toHaveBeenCalled();
+                saga.put(fileStorageDidFailToReadFile('test.file', testError));
 
                 await expect(saga.take()).resolves.toEqual(
-                    editorDidCloseFile('test.file'),
+                    editorDidFailToOpenFile('test.file', testError),
                 );
+
+                expect(OpenFileManager.prototype.add).not.toHaveBeenCalled();
+            });
+
+            describe('read succeeded', () => {
+                let model: monaco.editor.ITextModel;
+
+                beforeEach(async () => {
+                    monaco.editor.onDidCreateModel((m) => (model = m));
+
+                    saga.put(fileStorageDidReadFile('test.file', ''));
+
+                    expect(model).toBeDefined();
+
+                    await expect(saga.take()).resolves.toEqual(
+                        editorDidOpenFile('test.file'),
+                    );
+
+                    expect(OpenFileManager.prototype.add).toHaveBeenCalled();
+                    expect(OpenFileManager.prototype.remove).not.toHaveBeenCalled();
+                });
+
+                it('should close file if task is canceled', async () => {
+                    jest.spyOn(model, 'dispose');
+
+                    saga.cancel();
+
+                    // model should be disposed before fileStorageClose
+                    expect(model.dispose).toHaveBeenCalled();
+                    expect(OpenFileManager.prototype.remove).toHaveBeenCalled();
+
+                    // editorDidCloseFile is not called since we did not put editorCloseFile
+                });
+
+                it('should close when requested', async () => {
+                    jest.spyOn(model, 'dispose');
+
+                    saga.put(editorCloseFile('test.file'));
+
+                    // model should be disposed before fileStorageClose
+                    expect(model.dispose).toHaveBeenCalled();
+                    expect(OpenFileManager.prototype.remove).toHaveBeenCalled();
+
+                    await expect(saga.take()).resolves.toEqual(
+                        editorDidCloseFile('test.file'),
+                    );
+                });
             });
         });
     });
diff --git a/src/editor/sagas.ts b/src/editor/sagas.ts
index 5d826ef9..b753d551 100644
--- a/src/editor/sagas.ts
+++ b/src/editor/sagas.ts
@@ -5,6 +5,7 @@ import { monaco } from 'react-monaco-editor';
 import { EventChannel, buffers, eventChannel } from 'redux-saga';
 import {
     SagaGenerator,
+    call,
     delay,
     fork,
     getContext,
@@ -22,7 +23,7 @@ import {
     fileStorageWriteFile,
 } from '../fileStorage/actions';
 import { RootState } from '../reducers';
-import { defined, ensureError } from '../utils';
+import { acquireLock, defined, ensureError } from '../utils';
 import {
     editorActivateFile,
     editorCloseFile,
@@ -36,6 +37,7 @@ import {
     editorGetValueResponse,
     editorOpenFile,
 } from './actions';
+import { EditorError } from './error';
 import { ActiveFileHistoryManager, OpenFileManager } from './lib';
 import { pybricksMicroPythonId } from './pybricksMicroPython';
 
@@ -93,7 +95,7 @@ function* handleEditorOpenFile(
     let closeRequested = false;
 
     try {
-        const defer: Array<() => void> = [];
+        const defer: Array<() => void | Promise<void>> = [];
 
         try {
             const modelUri = monaco.Uri.from({
@@ -101,6 +103,19 @@ function* handleEditorOpenFile(
                 path: action.fileName,
             });
 
+            const releaseLock = yield* call(() =>
+                acquireLock(`pybricks.editor+${modelUri}`),
+            );
+
+            if (!releaseLock) {
+                throw new EditorError(
+                    'FileInUse',
+                    'the file is already open in another editor',
+                );
+            }
+
+            defer.push(releaseLock);
+
             yield* put(fileStorageReadFile(modelUri.fsPath));
 
             const { didRead, didFailToRead } = yield* race({
diff --git a/src/explorer/Explorer.test.tsx b/src/explorer/Explorer.test.tsx
index 4e489535..1696f508 100644
--- a/src/explorer/Explorer.test.tsx
+++ b/src/explorer/Explorer.test.tsx
@@ -9,13 +9,13 @@ import { FileMetadata } from '../fileStorage';
 import { useFileStorageMetadata } from '../fileStorage/hooks';
 import Explorer from './Explorer';
 import {
-    explorerActivateFile,
     explorerArchiveAllFiles,
     explorerCreateNewFile,
     explorerDeleteFile,
     explorerDuplicateFile,
     explorerExportFile,
     explorerImportFiles,
+    explorerUserActivateFile,
 } from './actions';
 
 afterEach(async () => {
@@ -74,7 +74,7 @@ describe('tree item', () => {
 
         userEvent.click(treeItem);
 
-        expect(dispatch).toHaveBeenCalledWith(explorerActivateFile('test.file'));
+        expect(dispatch).toHaveBeenCalledWith(explorerUserActivateFile('test.file'));
     });
 
     it('should dispatch action when key is pressed', async () => {
@@ -86,7 +86,7 @@ describe('tree item', () => {
         userEvent.click(treeItem);
         userEvent.keyboard('{enter}');
 
-        expect(dispatch).toHaveBeenCalledWith(explorerActivateFile('test.file'));
+        expect(dispatch).toHaveBeenCalledWith(explorerUserActivateFile('test.file'));
     });
 
     describe('duplicate', () => {
diff --git a/src/explorer/Explorer.tsx b/src/explorer/Explorer.tsx
index ad52851a..c7a50a71 100644
--- a/src/explorer/Explorer.tsx
+++ b/src/explorer/Explorer.tsx
@@ -31,13 +31,13 @@ import { useFileStorageMetadata } from '../fileStorage/hooks';
 import { isMacOS } from '../utils/os';
 import { TreeItemContext, TreeItemData, renderers } from '../utils/tree-renderer';
 import {
-    explorerActivateFile,
     explorerArchiveAllFiles,
     explorerCreateNewFile,
     explorerDeleteFile,
     explorerDuplicateFile,
     explorerExportFile,
     explorerImportFiles,
+    explorerUserActivateFile,
 } from './actions';
 import DeleteFileAlert from './deleteFileAlert/DeleteFileAlert';
 import DuplicateFileDialog from './duplicateFileDialog/DuplicateFileDialog';
@@ -373,7 +373,7 @@ const FileTree: React.VoidFunctionComponent<FileTreeProps> = ({ i18n }) => {
             canRename={false} // we implement our own rename handler
             onFocusItem={(item) => setFocusedItem(item.index)}
             onPrimaryAction={(item) =>
-                dispatch(explorerActivateFile(item.data.fileName))
+                dispatch(explorerUserActivateFile(item.data.fileName))
             }
         >
             <div className="pb-explorer-file-tree">
diff --git a/src/explorer/actions.ts b/src/explorer/actions.ts
index 0587427c..22ddf7a6 100644
--- a/src/explorer/actions.ts
+++ b/src/explorer/actions.ts
@@ -75,33 +75,20 @@ export const explorerDidFailToCreateNewFile = createAction((error: Error) => ({
  * Request to activate a file (open or bring to foreground if already open).
  * @param fileName The file name.
  */
-export const explorerActivateFile = createAction((fileName: string) => ({
-    type: 'explorer.action.activateFile',
+export const explorerUserActivateFile = createAction((fileName: string) => ({
+    type: 'explorer.user.action.activateFile',
     fileName,
 }));
 
 /**
- * Indicates that {@link explorerActivateFile} succeeded.
+ * Indicates that {@link explorerUserActivateFile} completed.
  * @param fileName The file name.
  */
-export const explorerDidActivateFile = createAction((fileName: string) => ({
-    type: 'explorer.action.didActivateFile',
+export const explorerUserDidActivateFile = createAction((fileName: string) => ({
+    type: 'explorer.user.action.didActivateFile',
     fileName,
 }));
 
-/**
- * Indicates that {@link explorerActivateFile} failed.
- * @param fileName The file name.
- * @param error The error that was raised.
- */
-export const explorerDidFailToActivateFile = createAction(
-    (fileName: string, error: Error) => ({
-        type: 'explorer.action.didFailToActivateFile',
-        fileName,
-        error,
-    }),
-);
-
 /**
  * Action that requests to duplicate a file.
  * @param fileName The file name.
diff --git a/src/explorer/alerts/FileInUseAlert.test.tsx b/src/explorer/alerts/FileInUseAlert.test.tsx
new file mode 100644
index 00000000..d4dec84f
--- /dev/null
+++ b/src/explorer/alerts/FileInUseAlert.test.tsx
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import React from 'react';
+import { testRender } from '../../../test';
+import { fileInUse } from './FileInUseAlert';
+
+it('should be valid', () => {
+    const callback = jest.fn();
+    const toast = fileInUse(callback, { fileName: 'test.file' });
+
+    // TODO: refactor this to a common function to be used by all alerts
+
+    // it should render
+    const [message] = testRender(<>{toast.message}</>);
+    expect(message).toBeDefined();
+
+    // it should have a dismiss callback
+    toast.onDismiss?.(false);
+    expect(callback).toHaveBeenCalledWith('dismiss');
+});
diff --git a/src/explorer/alerts/FileInUseAlert.tsx b/src/explorer/alerts/FileInUseAlert.tsx
new file mode 100644
index 00000000..b4da1782
--- /dev/null
+++ b/src/explorer/alerts/FileInUseAlert.tsx
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { Intent } from '@blueprintjs/core';
+import { useI18n } from '@shopify/react-i18n';
+import React from 'react';
+import { CreateToast } from '../../i18nToaster';
+import { I18nId } from './i18n';
+
+type FileInUseAlertProps = {
+    fileName: string;
+};
+
+const FileInUseAlert: React.VoidFunctionComponent<FileInUseAlertProps> = ({
+    fileName,
+}) => {
+    // istanbul ignore next: babel-loader rewrites this line
+    const [i18n] = useI18n();
+    return <>{i18n.translate(I18nId.FileInUseMessage, { fileName })}</>;
+};
+
+export const fileInUse: CreateToast<{ fileName: string }> = (
+    onAction,
+    { fileName },
+) => {
+    return {
+        message: <FileInUseAlert fileName={fileName} />,
+        icon: 'error',
+        intent: Intent.DANGER,
+        onDismiss: () => onAction('dismiss'),
+    };
+};
diff --git a/src/explorer/alerts/i18n.test.ts b/src/explorer/alerts/i18n.test.ts
new file mode 100644
index 00000000..e706ba28
--- /dev/null
+++ b/src/explorer/alerts/i18n.test.ts
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { lookup } from '../../../test';
+import { I18nId } from './i18n';
+import en from './translations/en.json';
+
+describe('Ensure .json file has matches for I18nId', () => {
+    test.each(Object.values(I18nId))('%s', (id) => {
+        expect(lookup(en, id)).toBeDefined();
+    });
+});
diff --git a/src/explorer/alerts/i18n.ts b/src/explorer/alerts/i18n.ts
new file mode 100644
index 00000000..8df7b63b
--- /dev/null
+++ b/src/explorer/alerts/i18n.ts
@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+export enum I18nId {
+    FileInUseMessage = 'fileInUse.message',
+}
diff --git a/src/explorer/alerts/index.ts b/src/explorer/alerts/index.ts
new file mode 100644
index 00000000..f5545974
--- /dev/null
+++ b/src/explorer/alerts/index.ts
@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { fileInUse } from './FileInUseAlert';
+
+// gathers all of the alert creation functions for passing up to the top level
+export default { fileInUse };
diff --git a/src/explorer/alerts/translations/en.json b/src/explorer/alerts/translations/en.json
new file mode 100644
index 00000000..73fb7d65
--- /dev/null
+++ b/src/explorer/alerts/translations/en.json
@@ -0,0 +1,5 @@
+{
+    "fileInUse": {
+        "message": "The file '{fileName}' could not be opened. It is already open in another window."
+    }
+}
diff --git a/src/explorer/sagas.test.ts b/src/explorer/sagas.test.ts
index 8f229e6f..f51e1224 100644
--- a/src/explorer/sagas.test.ts
+++ b/src/explorer/sagas.test.ts
@@ -5,6 +5,7 @@ import * as browserFsAccess from 'browser-fs-access';
 import { FileWithHandle } from 'browser-fs-access';
 import { mock } from 'jest-mock-extended';
 import { AsyncSaga } from '../../test';
+import { alertsShowAlert } from '../alerts/actions';
 import {
     editorActivateFile,
     editorCloseFile,
@@ -12,6 +13,7 @@ import {
     editorDidCloseFile,
     editorDidFailToActivateFile,
 } from '../editor/actions';
+import { EditorError } from '../editor/error';
 import {
     fileStorageCopyFile,
     fileStorageDeleteFile,
@@ -30,17 +32,14 @@ import {
 } from '../fileStorage/actions';
 import { pythonFileExtension } from '../pybricksMicropython/lib';
 import {
-    explorerActivateFile,
     explorerArchiveAllFiles,
     explorerCreateNewFile,
     explorerDeleteFile,
-    explorerDidActivateFile,
     explorerDidArchiveAllFiles,
     explorerDidCreateNewFile,
     explorerDidDeleteFile,
     explorerDidDuplicateFile,
     explorerDidExportFile,
-    explorerDidFailToActivateFile,
     explorerDidFailToArchiveAllFiles,
     explorerDidFailToCreateNewFile,
     explorerDidFailToDeleteFile,
@@ -51,6 +50,8 @@ import {
     explorerDuplicateFile,
     explorerExportFile,
     explorerImportFiles,
+    explorerUserActivateFile,
+    explorerUserDidActivateFile,
 } from './actions';
 import {
     deleteFileAlertDidAccept,
@@ -243,25 +244,40 @@ describe('handleExplorerActivateFile', () => {
     beforeEach(async () => {
         saga = new AsyncSaga(explorer);
 
-        saga.put(explorerActivateFile('test.file'));
+        saga.put(explorerUserActivateFile('test.file'));
 
         await expect(saga.take()).resolves.toEqual(editorActivateFile('test.file'));
     });
 
-    it('should propagate error', async () => {
+    it('should alert file in use error', async () => {
+        const testError = new EditorError('FileInUse', 'test error');
+        saga.put(editorDidFailToActivateFile('test.file', testError));
+
+        await expect(saga.take()).resolves.toEqual(
+            alertsShowAlert('explorer', 'fileInUse', { fileName: 'test.file' }),
+        );
+        await expect(saga.take()).resolves.toEqual(
+            explorerUserDidActivateFile('test.file'),
+        );
+    });
+
+    it('should alert unexpected error', async () => {
         const testError = new Error('test error');
         saga.put(editorDidFailToActivateFile('test.file', testError));
 
         await expect(saga.take()).resolves.toEqual(
-            explorerDidFailToActivateFile('test.file', testError),
+            alertsShowAlert('alerts', 'unexpectedError', { error: testError }),
+        );
+        await expect(saga.take()).resolves.toEqual(
+            explorerUserDidActivateFile('test.file'),
         );
     });
 
-    it('should propagate success', async () => {
+    it('should notify success', async () => {
         saga.put(editorDidActivateFile('test.file'));
 
         await expect(saga.take()).resolves.toEqual(
-            explorerDidActivateFile('test.file'),
+            explorerUserDidActivateFile('test.file'),
         );
     });
 
diff --git a/src/explorer/sagas.ts b/src/explorer/sagas.ts
index f6c9bc98..dd0e5e7b 100644
--- a/src/explorer/sagas.ts
+++ b/src/explorer/sagas.ts
@@ -4,6 +4,7 @@
 import { fileOpen, fileSave } from 'browser-fs-access';
 import JSZip from 'jszip';
 import { call, put, race, take, takeEvery } from 'typed-redux-saga/macro';
+import { alertsShowAlert } from '../alerts/actions';
 import {
     editorActivateFile,
     editorCloseFile,
@@ -11,6 +12,7 @@ import {
     editorDidCloseFile,
     editorDidFailToActivateFile,
 } from '../editor/actions';
+import { EditorError } from '../editor/error';
 import { getPybricksMicroPythonFileTemplate } from '../editor/pybricksMicroPython';
 import {
     fileStorageCopyFile,
@@ -38,17 +40,14 @@ import {
 } from '../pybricksMicropython/lib';
 import { defined, ensureError, timestamp } from '../utils';
 import {
-    explorerActivateFile,
     explorerArchiveAllFiles,
     explorerCreateNewFile,
     explorerDeleteFile,
-    explorerDidActivateFile,
     explorerDidArchiveAllFiles,
     explorerDidCreateNewFile,
     explorerDidDeleteFile,
     explorerDidDuplicateFile,
     explorerDidExportFile,
-    explorerDidFailToActivateFile,
     explorerDidFailToArchiveAllFiles,
     explorerDidFailToCreateNewFile,
     explorerDidFailToDeleteFile,
@@ -59,6 +58,8 @@ import {
     explorerDuplicateFile,
     explorerExportFile,
     explorerImportFiles,
+    explorerUserActivateFile,
+    explorerUserDidActivateFile,
 } from './actions';
 import {
     deleteFileAlertDidAccept,
@@ -226,11 +227,11 @@ function* handleExplorerCreateNewFile(): Generator {
  * @param action
  */
 function* handleExplorerActivateFile(
-    action: ReturnType<typeof explorerActivateFile>,
+    action: ReturnType<typeof explorerUserActivateFile>,
 ): Generator {
     yield* put(editorActivateFile(action.fileName));
 
-    const { didActivate, didFailToActivate } = yield* race({
+    const { didFailToActivate } = yield* race({
         didActivate: take(
             editorDidActivateFile.when((a) => a.fileName === action.fileName),
         ),
@@ -240,18 +241,23 @@ function* handleExplorerActivateFile(
     });
 
     if (didFailToActivate) {
-        yield* put(
-            explorerDidFailToActivateFile(
-                didFailToActivate.fileName,
-                didFailToActivate.error,
-            ),
-        );
-        return;
+        if (
+            didFailToActivate.error instanceof EditorError &&
+            didFailToActivate.error.name === 'FileInUse'
+        ) {
+            yield* put(
+                alertsShowAlert('explorer', 'fileInUse', { fileName: action.fileName }),
+            );
+        } else {
+            yield* put(
+                alertsShowAlert('alerts', 'unexpectedError', {
+                    error: didFailToActivate.error,
+                }),
+            );
+        }
     }
 
-    defined(didActivate);
-
-    yield* put(explorerDidActivateFile(didActivate.fileName));
+    yield* put(explorerUserDidActivateFile(action.fileName));
 }
 
 /** Connects user initiate duplicate file actions to the duplicate file dialog. */
@@ -380,7 +386,7 @@ export default function* (): Generator {
     yield* takeEvery(explorerArchiveAllFiles, handleExplorerArchiveAllFiles);
     yield* takeEvery(explorerImportFiles, handleExplorerImportFiles);
     yield* takeEvery(explorerCreateNewFile, handleExplorerCreateNewFile);
-    yield* takeEvery(explorerActivateFile, handleExplorerActivateFile);
+    yield* takeEvery(explorerUserActivateFile, handleExplorerActivateFile);
     yield* takeEvery(explorerDuplicateFile, handleExplorerDuplicateFile);
     yield* takeEvery(explorerExportFile, handleExplorerExportFile);
     yield* takeEvery(explorerDeleteFile, handleExplorerDeleteFile);
diff --git a/src/notifications/I18nToaster.tsx b/src/i18nToaster.tsx
similarity index 55%
rename from src/notifications/I18nToaster.tsx
rename to src/i18nToaster.tsx
index d7094575..72829afc 100644
--- a/src/notifications/I18nToaster.tsx
+++ b/src/i18nToaster.tsx
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
-// Copyright (c) 2021 The Pybricks Authors
+// Copyright (c) 2021-2022 The Pybricks Authors
 
-import { IToaster, Toaster } from '@blueprintjs/core';
+import { IToastProps, IToaster, Toaster } from '@blueprintjs/core';
 import { I18nContext, I18nManager } from '@shopify/react-i18n';
 import React from 'react';
 import ReactDOM from 'react-dom';
@@ -34,3 +34,24 @@ export function create(i18n: I18nManager): IToaster {
 
     return toaster.current;
 }
+
+/**
+ * Template type alert callbacks.
+ *
+ * This is called when an alert is dismissed.
+ *
+ * @param action: The action that the user selected. This is usually 'dismiss'.
+ */
+export type ToastActionHandler<A extends string> = (action: A) => void;
+
+/**
+ * Template type for all toast creation functions for alert components.
+ *
+ * @param onAction A callback that is called when the toast is dismissed.
+ * @param props Additional properties required by this toast, if any (usually
+ * replacements for translations).
+ */
+export type CreateToast<
+    P extends Record<string, unknown> = never,
+    A extends string = 'dismiss',
+> = (onAction: ToastActionHandler<A>, props: P) => IToastProps;
diff --git a/src/index.tsx b/src/index.tsx
index 6c751040..336a6e1a 100644
--- a/src/index.tsx
+++ b/src/index.tsx
@@ -14,7 +14,7 @@ import App from './app/App';
 import { appVersion } from './app/constants';
 import { db } from './fileStorage/context';
 import { i18nManager } from './i18n';
-import * as I18nToaster from './notifications/I18nToaster';
+import * as I18nToaster from './i18nToaster';
 import { rootReducer } from './reducers';
 import reportWebVitals from './reportWebVitals';
 import rootSaga, { RootSagaContext } from './sagas';
@@ -30,6 +30,7 @@ const sagaMiddleware = createSagaMiddleware<RootSagaContext>({
         notification: { toaster },
         terminal: defaultTerminalContext,
         fileStorage: db,
+        toaster,
     },
 });
 
diff --git a/src/notifications/i18n.ts b/src/notifications/i18n.ts
index 70703bba..7ac7e55b 100644
--- a/src/notifications/i18n.ts
+++ b/src/notifications/i18n.ts
@@ -5,9 +5,6 @@
 
 export enum I18nId {
     AppNoUpdateFound = 'app.noUpdateFound',
-    CopyErrorMessage = 'copyErrorMessage',
-    TechnicalInfo = 'technicalInfo',
-    ReportBug = 'reportBug',
     BleUnexpectedError = 'ble.unexpectedError',
     BleGattPermission = 'ble.gattPermission',
     BleGattServiceNotFound = 'ble.gattServiceNotFound',
diff --git a/src/notifications/sagas.test.ts b/src/notifications/sagas.test.ts
index ead5bdd9..cb5381bb 100644
--- a/src/notifications/sagas.test.ts
+++ b/src/notifications/sagas.test.ts
@@ -32,6 +32,7 @@ import {
     MetadataProblem,
     didFailToFinish,
 } from '../firmware/actions';
+import * as i18nToaster from '../i18nToaster';
 import {
     BootloaderConnectionFailureReason,
     didFailToConnect as bootloaderDidFailToConnect,
@@ -41,14 +42,13 @@ import {
     serviceWorkerDidSucceed,
     serviceWorkerDidUpdate,
 } from '../service-worker/actions';
-import * as I18nToaster from './I18nToaster';
 import { add } from './actions';
 import { I18nId } from './i18n';
 import notification from './sagas';
 
 function createTestToasterSaga(): { toaster: IToaster; saga: AsyncSaga } {
     const i18n = new I18nManager({ locale: 'en' });
-    const toaster = I18nToaster.create(i18n);
+    const toaster = i18nToaster.create(i18n);
 
     jest.spyOn(toaster, 'clear');
     jest.spyOn(toaster, 'dismiss');
diff --git a/src/notifications/sagas.ts b/src/notifications/sagas.ts
index aae175db..92f26458 100644
--- a/src/notifications/sagas.ts
+++ b/src/notifications/sagas.ts
@@ -10,6 +10,7 @@ import React from 'react';
 import { channel } from 'redux-saga';
 import * as semver from 'semver';
 import { delay, getContext, put, take, takeEvery } from 'typed-redux-saga/macro';
+import { getAlertProps } from '../alerts';
 import { appDidCheckForUpdate, appReload } from '../app/actions';
 import { appName } from '../app/constants';
 import { bleDIServiceDidReceiveFirmwareRevision } from '../ble-device-info-service/actions';
@@ -18,6 +19,7 @@ import {
     didFailToConnect as bleDeviceDidFailToConnect,
 } from '../ble/actions';
 import { editorDidFailToOpenFile } from '../editor/actions';
+import { EditorError } from '../editor/error';
 import {
     explorerDidFailToArchiveAllFiles,
     explorerDidFailToCreateNewFile,
@@ -37,7 +39,6 @@ import { serviceWorkerDidUpdate } from '../service-worker/actions';
 import { pythonVersionToSemver } from '../utils/version';
 import NotificationAction from './NotificationAction';
 import NotificationMessage from './NotificationMessage';
-import UnexpectedErrorNotification from './UnexpectedErrorNotification';
 import { add as addNotification } from './actions';
 import { I18nId } from './i18n';
 
@@ -159,14 +160,15 @@ function* showSingleton(
 }
 
 /** Shows a special notification for unexpected errors. */
-function* showUnexpectedError(messageId: I18nId, err: Error): Generator {
+function* showUnexpectedError(messageId: I18nId, error: Error): Generator {
     const { toaster } = yield* getContext<NotificationContext>('notification');
-    toaster.show({
-        intent: mapIntent(Level.Error),
-        icon: mapIcon(Level.Error),
-        message: React.createElement(UnexpectedErrorNotification, { messageId, err }),
-        timeout: 0,
-    });
+    const key = `alerts.unexpectedError.${messageId}`;
+
+    toaster.show(
+        getAlertProps('alerts', 'unexpectedError', () => toaster.dismiss(key), {
+            error,
+        }),
+    );
 }
 
 function* showBleDeviceDidFailToConnectError(
@@ -441,9 +443,12 @@ function* showExplorerFailToExport(
 }
 
 function* showEditorDidFailToOpenFile(
-    action: ReturnType<typeof explorerDidFailToExportFile>,
+    action: ReturnType<typeof editorDidFailToOpenFile>,
 ): Generator {
-    // TODO: add a better error message for the case where a file is already in use
+    if (action.error instanceof EditorError && action.error.name === 'FileInUse') {
+        return;
+    }
+
     yield* showUnexpectedError(I18nId.EditorFailedToOpenFile, action.error);
 }
 
diff --git a/src/notifications/translations/en.json b/src/notifications/translations/en.json
index 882c87d5..15ed39f6 100644
--- a/src/notifications/translations/en.json
+++ b/src/notifications/translations/en.json
@@ -1,7 +1,4 @@
 {
-    "copyErrorMessage": "Copy Error Message",
-    "technicalInfo": "Expand for detailed technical information",
-    "reportBug": "Report Bug",
     "app": {
         "noUpdateFound": "{appName} is already up to date."
     },
diff --git a/src/sagas.ts b/src/sagas.ts
index 5f8a823e..59adb9a1 100644
--- a/src/sagas.ts
+++ b/src/sagas.ts
@@ -2,6 +2,7 @@
 // Copyright (c) 2020-2022 The Pybricks Authors
 
 import { all, put } from 'typed-redux-saga/macro';
+import alerts, { AlertsSagaContext } from './alerts/sagas';
 import { didStart } from './app/actions';
 import app from './app/sagas';
 import blePybricksService from './ble-pybricks-service/sagas';
@@ -21,6 +22,7 @@ import terminal, { TerminalSagaContext } from './terminal/sagas';
 /* istanbul ignore next */
 export default function* (): Generator {
     yield* all([
+        alerts(),
         app(),
         blePybricksService(),
         ble(),
@@ -44,6 +46,7 @@ export default function* (): Generator {
  */
 export type RootSagaContext = {
     nextMessageId: () => number;
-} & FileStorageSageContext &
+} & AlertsSagaContext &
+    FileStorageSageContext &
     NotificationSagaContext &
     TerminalSagaContext;