I recently purchased several of these TrackR Bravo devices online after hearing great things about them.
They use Crowd GPS technology (to learn more about Crowd GPS click Here) and have a tone/ringer, phone finder app for google play or the app store, and separation alerts.
I’ve placed these nifty devices in and on several of my items, bicycle, backpack, vehicle, keys, etc. The battery life is fairly good, I have had to replace one battery about 2 months after purchasing and using the TrackR Bravo.
If you’d like to order some you can get them online here