Toggle alarm to scare intruders?
Might be interesting if you have a MacBook...

http://mac360.com/2011/05/free-add-motion-detector-security-to-your-mac/


  iAlertU is an alarm system for your Apple MacBook that uses the built
  in motion detection to trigger the alarm and the iSight to capture the
  image of the thief. Among many other features, it incorporates the
  ability for users with iPhone, iPad, or iPod Touch to connect to and
  control iAlertU remotely.