Prey lets you keep track of your phone or laptop at all times, and will help you find it if it ever gets lost or stolen.
It's lightweight, open source software, and free for anyone to use. And it just works.
Basically you install a tiny agent in your PC or phone, which silently waits for a remote signal to wake up and work its magic.
This signal is sent either from the Internet or through an SMS message, and allows you to gather information regarding the device's location, hardware and network status, and optionally trigger specific actions on it.