diff --git a/RTClib.cpp b/RTClib.cpp
index b3c8a70..4160f7e 100644
--- a/RTClib.cpp
+++ b/RTClib.cpp
@@ -755,13 +755,16 @@ static uint8_t bin2bcd(uint8_t val) { return val + 6 * (val / 10); }
 
 /**************************************************************************/
 /*!
-    @brief  Startup for the DS1307
-    @return Always true
+    @brief  Start I2C for the DS1307 and test succesful connection
+    @return True if Wire can find DS1307 or false otherwise.
 */
 /**************************************************************************/
 boolean RTC_DS1307::begin(void) {
   Wire.begin();
-  return true;
+  Wire.beginTransmission(DS1307_ADDRESS);
+  if (Wire.endTransmission() == 0)
+    return true;
+  return false;
 }
 
 /**************************************************************************/
@@ -995,13 +998,16 @@ DateTime RTC_Micros::now() {
 
 /**************************************************************************/
 /*!
-    @brief  Start using the PCF8523
-    @return True
+    @brief  Start I2C for the PCF8523 and test succesful connection
+    @return True if Wire can find PCF8523 or false otherwise.
 */
 /**************************************************************************/
 boolean RTC_PCF8523::begin(void) {
   Wire.begin();
-  return true;
+  Wire.beginTransmission(PCF8523_ADDRESS);
+  if (Wire.endTransmission() == 0)
+    return true;
+  return false;
 }
 
 /**************************************************************************/
diff --git a/examples/pcf8523/pcf8523.ino b/examples/pcf8523/pcf8523.ino
index b008105..45e75c8 100644
--- a/examples/pcf8523/pcf8523.ino
+++ b/examples/pcf8523/pcf8523.ino
@@ -14,6 +14,7 @@ void setup () {
 
   if (! rtc.begin()) {
     Serial.println("Couldn't find RTC");
+    Serial.flush(); // ensure above text prints with nRF52 native USB Serial
     while (1);
   }
 
diff --git a/examples/pcf8523Countdown/pcf8523Countdown.ino b/examples/pcf8523Countdown/pcf8523Countdown.ino
index b670521..0ca5e36 100644
--- a/examples/pcf8523Countdown/pcf8523Countdown.ino
+++ b/examples/pcf8523Countdown/pcf8523Countdown.ino
@@ -41,6 +41,7 @@ void setup () {
 
   if (! rtc.begin()) {
     Serial.println("Couldn't find RTC");
+    Serial.flush(); // ensure above text prints with nRF52 native USB Serial
     while (1);
   }