A simple invisible utility that regularly 'calls' home. It sends information back to a web server that could help identify your computer's location if it is stolen.
Tickle works whether a user is logged in or not, as long as the computer has an internet connection. It does so by looking up a http url in the form: http://www.yourdomain.com/tickle.htm?mac_addr You can then look for the IP address with that MAC address in your web server logs to help the authorities locate your computer if it's stolen. You may customise the scripts to add alerts and other actions.