Presence by People Power is a free iOS app that transforms an iPhone, iPod, or iPad into a home security video monitor. The camera can be activated manually or by utilizing the motion detecting software within the app. People Power, the company behind the app, sees the app as a great way of re-using old iOS devices. For example, if you just upgraded to an iPhone 5, use your old iPhone 4 as a security camera.
The app requires iOS 5.0 or later and is compatible with iPhone 3GS, iPhone 3GS, iPhone 4, iPhone 4S, iPhone 5, iPod touch (3rd gen), iPod touch (4th gen), iPod touch (5th gen) and iPad.