If you have been looking for a DIY project to kill time, then the Zippo Burglar Alarm here might be just the ticket. After all, it is small enough to fit into any pocket considering its original size, but just make sure nobody around you asks for a light lest you give the game away. Based on a Picaxe microcontroller that controls a few IR LEDs and while monitoring an IR Receiver module, the alarm itself is a piezo buzzer which has also been mounted within such a small amount of space. It will send out a modulated infrared signal, waiting for the detector to sense whether there are any reflected signals. If the answer is in the affirmative, then it will “know” that someone has passed by. Powered by a trio of AG-13 button cell batteries, it has a working range of around 15cm under ideal conditions – not perfect, but decent enough to work behind closed doors.