Lookout provides some security features that can locate your phone in case you lose it, can wipe it remotely it case it was lost, etc. If you have an iPhone, some of the features are offered by Apple as part of there iCloud service, but iCloud has had some stability issues in the past, and as far as security goes, redundancy is a good thing. Lookout is a free service/app, although paid plans offer additional features. This is an app you hope you will never have to use, but will be happy to have it in case you need it.