I need a device that will be able to track my mom's phone when she loses it. She has lost 4 phones now. She is the absent minded professor when it comes to phones. She doesn't use it a lot so she doesn't care about it. I'd like to get her a tracker of some sort to put on her phone so she can find it when it is dead. Usually she doesn't know it is lost until it is dead.

Suggestions? It can't be an app on the phone because the phone needs to be found when not charged.