A service call from a professional locksmith can cost well over $100 - plus the inconvenience (and embarrassment) of locking yourself out of home or car. Simple to install - just find a hidden area of metal that attracts the magnet (Hint: if the metal has rust, that means it contains iron and is 'ferrous'). Clean/brush the surface slightly so the magnet makes strong contact. If you're attaching to a vehicle, pick a spot that isn't directly exposed to water or sand sprayed from the wheels. Also, a handy way to 'exchange' keys if someone else needs to pick-up a vehicle at the airport, etc.