Personal Angel is an open source hardware and software multicopter project designed to provide personal assistance coverage of cities, university campuses, business parks, and suburbs through a mesh network of Personal Angels.

You've ended your shift at work at 3am, and are walking home. There's a person walking behind you that's creeping you out. You can't call family as it's 3am, and you can't call the police either because nothing's happened - it's just someone else walking on the street at this point. But if something does happen, and the situation escalates, it'll be too late to make that call.

This is where Personal Angel shines. You place a request, and the closest Personal Angel in the mesh network is sent to your location to monitor you. If the situation does escalate, it calls police or family to get you the assistance you need - and otherwise it just provides a reassuring presence, and deterrent to anything happening in the first place.