Thieves make off with millions of dollars’ worth of laptops and mobile devices every year. Most stolen gadgets go unrecovered, but tracking software can help. The software runs in the background of the operating system or, with some services, the boot-level layer, which makes detecting the tracker much more difficult. Services like Prey provide free software for up to three laptops or Android devices. BlackBerry, iPhone or iPad owners can use GadgetTrak(from $4).