If you're a person who finds it difficult finding their keys, Hone is your saviour. Hone is a neat little device which you attach to your keys, when you can't find your keys, you launch the Hone app on your iPhone and the Hone keyring will light up, vibrate and make sounds to help you find your keys. It runs for 6 months on its battery and has a range of 150+ feet.
It will only work with the iPhone 4S though because that is the only iPhone to use Bluetooth 4.0 which uses a lot less power than previous generations.
It's not for sale yet because its a Kickstarter project. However it will definitely go on sale now because it has beaten its $46,000 target and has still got 24 days to go. So who knows how much it will end up getting. If you're interested in getting one before anyone else you just have pledge $40 to the project if you're in the US, or $55 if you're outside the US.