Tickle is 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 using a Web server to look for 'tickles' from a stolen computer. When a tickle is received, the Web server will send you an email message containing its current IP address.