Prey can be used with an online control panel at Preyproject.com or, if you are an advanced user, you can use your own web server and receive reports via email. In case your laptop is stolen or lost, you can activate the signal from the control panel or, if using your own server, delete a special HTML file on your server to cause Prey to start sending reports.
The online control panel offers more functionality than the advanced method and it is free to use with up to 3 devices and 10 concurrent reports. Prey is also available for Linux, Mac and Android phones.
Needless to say, Prey only works if the missing device is connected to the Internet.