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 uses either the device's GPS or the nearest WiFi hotspots to triangulate and grab a fix on the location of your device. Prey even allows you to display a message which will show that the device is being tracked or you can completely lock down your system. It supports various popular operating systems including Windows, Mac and Android. Best of all Prey is lightweight, open source software, and free for anyone to use.