Imagine you were James Bond, an international spy who must always be keeping an eye on intruders.  You are at a secret location and you need to be able to tell if someone is at the front door, you can get a bunch of these portable Zippo lighter alarms placed at where you need to be alerted. Hey, maybe it’s still useful if you are not a spy, you can use it to tell when your cat walks through the cat door too. via hackedgadgets, Project Page