Description
Returns the next byte (character) of incoming serial data without removing it from the internal serial buffer. That is, successive calls to peek() will return the same character, as will the next call to read(). peek() inherits from the Stream utility class.
Syntax
Serial.peek()
Arduino Mega only:
Serial1.peek()
Serial2.peek()
Serial3.peek()
Parameters
Nothing
Returns
The first byte of incoming serial data available (or -1 if no data is available) - int