Tile - cornelltech/device-library GitHub Wiki
When you attach Tile to an item (like your keys), you're really tethering them both to your phone. So when your stuff gets lost, it has a buddy that knows what to do. Tile casts a Bluetooth signal up to 100 feet, making short work of any haystacks you lose your needles in. And since every phone with Tile helps find your stuff, your search range is potentially limitless.
Price: $180
Website: https://www.thetileapp.com/