I've been hearing more and more about the Arduino microcontroller project lately, and this is by far one of the coolest uses for it I've seen. Arduino is an open-source hardware project meant for easy prototyping of hardware ideas. This is Steve Hoefer's great vision for a mechanism that opens a door when it detects a secret knock. Here it is in action:
As you can see, he's programmed the microcontroller to listen for a specific knock sequence. When it hears it, it turns the deadbolt, meaning you can open the door. It's a simple but genius idea.
We're hoping something like this comes to market. Sure, it's not the most secure idea in the world, but it's fun enough that it'd be great for the inside of homes or backyard sheds or underground sex dungeons.