I'm not going to try to relate this to fitness, but nobody likes losing stuff.
There are several tracking devices on the market that keep up with your keys and wallet, but Tile is by far the best choice. The Tile app is what really sets it apart, allowing you to see exactly where your valuables are on the map at any given time. Tile also has a subscription that includes a new Tile every year so you never have to worry about low batteries or devices being incompatible because they're out of date.