Never lose your keys again.
If you have an iOS device, you really owe it to yourself to pick up one of these Elgato Smart Keys.
No magic here, it's just a little device the size of a key ring, with a long-lasting and cheap-to-replace battery that has one purpose in life. If you lose your keys, and you're within Bluetooth range, it will help you find them. No it won't help you much if you left them on the subway, but if you are the sort of person who walks around the house aimlessly, hoping you can find your car keys before you're late... what are you waiting for?
There's an app (of course) which is why you need an iOS device. It's simple and easy to use, and if you tell your phone to do so, it will make your keychain beep until you find it.
Oh, there's another little trick, too -- If you leave the app running it will tell you if you leave your keys behind with plenty of time to go get them (unless, you know, they're in a moving subway.
The price is right and the time is now... shop now at Solid Signal!