Zoombak GPS pet and vehicle locators make tracking your stuff easy
Sure, they are designed to use on your vehicle or pet, and at $199 to $249 it would have to be something roughly that important to be worth it, but you could probably use it for whatever you wanted. Don't worry, I don't think they'll ask too many questions when you buy one.
Regardless, they are smaller than a deck of cards, and they only weigh 3 ounces, which must be close to a record low weight for some GPS hardware. After you set them up and put them on your car or dog you can get location info by text message or email.
So, if you live in a city or drive a vehicle that makes theft likely this could be a good investment. Also, if you really love your dog, or if it cost a lot, you might find this a valuable investment. Personally, I could see myself using them for far less honorable purposes, I don't know how yet, but I'd find a way, because I have a piece of crap car that no one is going to steal (I rarely ever even bother removing the keys) and I don't have any pets.