Having worked seven summers at a golf club, I've spent plenty of time searching for lost keys and wallets on the course or in the clubhouse. If only the folks at Tile had been around earlier.
The company has developed its small square device, which can be hung on a key ring or taped to a wallet, to track down misplaced items. Download the Tile app, which uses the Bluetooth on your iPhone/iPad. If the Tile is within range (about 150 feet), an indicator will tell you when you're getting close. You can also hit the "find" button, and the Tile will play a song to help you hear where it is. For Tiles out of range, the app shows the last place it was able to detect the Tile (and when).
The first wave of Tiles sold out, but you can pre-order them for $20 this fall on thetileapp.com.