Okay. Which ones did you test? Having asked that question, i can't think of an app that would prevent the theft of a device. There are numerous apps that can assist in the recovery of a stolen device and one of those apps is Apple's own "Find My iPhone" app. "Look-out" is another one that's been around a while and works well. Still, the best defense against theft is to prevent the device from being the position of being stolen, in my opinion.