Here’s a pretty simple burglar alarm you can make and toss in your car/desk drawer/whatever, it uses the handy dandy 555 timer chip… – “In this auto shut off tone generator project, once the switch to the 9V power supply is connected, the alarm will trigger at a frequency of approximately 1.27 kHz. It will remain ON for a duration of approximately 170 seconds or 2.8 minutes before it stopped. This is a typical home burglar alarm system of which once the alarm is triggered ON, it will not be shut OFF until the duration of time set has elapsed. This project is useful when built as one can carry it along wherever one goes or placed it in a vehicle. In times of emergency, one can easily switched ON the switch and the loud speaker will emit a loud sound that will frighten the uninvited guest.” – Link.