Apple's AirTag is a small, disk-shaped tracking device that can be slipped inside or attached to your valuables via AirTag accessories. Using the Find My app, you can track down the AirTag and whatever item you've attached it to. The AirTag's battery is easily replaceable. Best of all, you don't have to take it to your local Apple Store to replace it. You can easily do it at home without any tools. The replacement battery costs only a few bucks and can be found in just about any store that carries batteries.