This project forms one of the most inventive door-locking systems we’ve ever seen. Created by Rob Hemsley at MIT, it is a combination lock of sorts – but instead of using a numeric keypad or dial – the unlocking is activated by knocking on the door handle in a pre-determined pattern. It sounds crazy but can work very well once the user has been trained.
How it works is quite simple. The only caveat is that the door handle must be metal as it must be able to conduct electricity. An Arduino board is connected to a piece of copper plating which is attached to the door handle fixture. This turns the door handle into a capacitive touch sensor. Therefore when the handle is touched – the Arduino can detect this.
The “combination” for entry is a sequence of touches with predetermined periods of time between each knock. So for entry a person must touch the door handle several times matching this pattern. If successful, the Arduino will control a servo to unlock the door lock mechanism on the rear of the handle. Simple, yet ingenious. You can see the lock in action via the following video:
Finally the cost of creating such a lock – if you already have a suitable doorknob – could easily fall under $50. So for more information and to make your own, visit the project page http://www.robhemsley.co.uk/knock_lock.htm