Tile (@TheTileApp) is an absolutely brilliant hardware device that can be attached to keys (or just about anything) so that you can locate them when lost. Tiles measures 36mm x 36mm x 4.2mm (or about the size of a matchbook), uses Bluetooth 4.0 (low energy) and will be compatible with iPhone 4S, iPhone 5, iPad Mini, iPad 3rd and 4th generation, and iPod Touch 5th generation. (Sorry Android users).
Bluetooth 4.0 is a brilliant choice because the built-in battery lasts about a year and doesn't require recharging. While GPS would be ideal, it suffers from heavy battery consumption (less than a day, typically) and WiFi requires open hotspot access.
The Tile iOS app (not yet available) allows your to find a Tile by telling you how close you are to it. You can see yourself getting closer and further away from the Tile when within a 50 - 150ft range via the iOS app. The app logs the last location it saw your Tile (via GPS) giving you a good starting point. Tile also includes a built-in speaker, so you can make it emit a tone when you're getting close.
But it's the Tile service that makes it compelling. It uses a crowd-sourced model so that you still have a good chance of finding your Tile (when it's attached to a dog or your MacBook, for example) even when it travels out of its 150-foot (Bluetooth) range. It's like having the world help you locate your lost item. You can track a Tile by seeing when it's identified by other Tile users.
Obviously the service requires a large user base to be effective (and may not work in less populated areas) but it's a no brainer in large metros. And something tells me that the service will gain critical mass quickly.
Even though you're helping find other people's Tiles with your iPhone, the company insists that it takes your security seriously. Other Tile users cannot search for your Tiles (or your iPhone) for example and only you and the Tile users you've explicitly shared your Tiles with can search for your Tiles.
A single Tile can be pre-ordered for $19 and quantities of four or higher cost around $14 each and will ship in "winter 2013/14" according to the developers (SRP will be $25 post launch). I pre-ordered eight (there's a limit of 10 Tiles per account) so that I can attach them to all of my devices and maybe a few non-gadgets as well.
How much would you pay to find your keys in a crunch? What about your MacBook?