I saw this car commercial involving a guy in his parking lot trying to find his car, and it made me think, why don't the guys just put a little LCD on your keychain that points you in the direction of your car? After all, your keychain is already tailor-made for your car, what with the remote unlocking/engine starting features, right? I'm giving this idea out for free, because I'm too lazy to go patent it and get rich off of it. I'll be satisfied knowing that I may have contributed to making the world a better place.

For the gritty details of how it would work, I'd figure you'd have eight sensors in your keychain, arranged in the eight cardinal directions. The number eight might not be critical, but eight makes it easy to visualize, which is why I picked that number. I'll number the eight directions the same way your computer numeric pad is numbered, so the 4 is left and 6 is right and 8 is forwards and 2 is backwards. When you press the "locate car" button, your keychain sends out a signal saying it wants your car to respond. When your car responds, the signal it sends is picked up by all eight sensors. The sensor that picked it up first is the direction your car is in. If all you want is the direction your car is in, this should be enough, but if you also want range, that could also be possible.

If you're right next to your car, then when it sends a signal out, that spreads in the form of the surface of a sphere, right? Notice that the sensors are spaced apart in an fixed way (say 1 centimeter). The curvature of an arc with a 1 centimeter chord of a small sphere is much higher than the curvature of an arc with a 1centimeter chord of a big sphere. Let's say the sensor 9 is triggered first, followed, a little later, but sensors 8 and 6. That means that the direction is forward and to the right of you, and is very near. If 8 and 6 are triggered almost immediately after 9 is triggered, then the curvature of the signal sphere must be very small, and so the car is far from you.