Best Buy via eBay offers the Tile Mate Bluetooth Tracker 4-Pack for $39.99 with free shipping. (Amazon, P.C. Richard and Son, and Tile charge the same.) That's $8 under our January mention, $10 each, and the lowest per-unit price we've seen. (It's the best deal for a 4-pack now by $10.) It attaches to something that you don't want to lose, such as keys or a backpack, and can be tracked from Tile's iOS and Android apps.