Now that you have a means of sending email from your Arduino, this opens up all sorts of possibilities You could add different types of sensor, and perhaps send yourself hourly temperature reports by email.

The PIR sensor could be used directly with the Arduino to play a warning tone or turn on LEDs.

About the Author.

Simon Monk is author of a number of books relating to Open Source Hardware. The following books written by Simon are available from Adafruit: Programming Arduino, 30 Arduino Projects for the Evil Genius and Programming the Raspberry Pi.