Forget secret handshakes, this nifty little detector actually recognizes a series of coded “door knocks” and instantly unlocks your door.
Move over retinal and fingerprint scanners, the latest in personal identification devices is this door knock detector, made from Arduino hardware, PVC pipes, and other bits and pieces programmer Steve Hoefer found in his tech lab.
Basically, the detector works by recording and counting time between a series of knocks and then unlocking your door. Simple enough, right?
According to Make:
Of course, this system is susceptible to a replay attack, because anyone can listen to the knock pattern and then know how to get in.
If you are planning to use something like this, I would recommend either incorporating a timestamp into the message, or using a series of one time knocks, in order to make it harder to break into. Actually, that might make it more secure than a regular lock.