GPS Tracking

You are supposed to be able to track cell phones, perhaps a "family plan?" I don't know how you do so without a smart phone. If you can hide it so it has a backup battery, that will give you "a little time" before it's stripped and found.
There is an app called "Find my friends" in the Play Store, download it into the hidden phone and your smart phone, it uses GPS to locate you and your "friend" and displays the location on a map and it is fairly accurate. Granted both phones still need cell service, but as far as a battery backup, a hidden car phone charger hard wired to a live car battery circuit and plugged into the "hidden" phone should keep that phone going for a very long time.

I have a couple of friends myself and the wife in my "group", I just looked at the app and it shows me that the wife and I are home with the markers over our home.