A secret knock can get you into a lot of places. This is the first time that we have seen a knock which could actually open a lock automatically. Steve Hoefer came up with this ingenious way of unlocking his front door to anyone who knows the right code.
Steve Hoefer's device unlocks your front door whenever someone makes the appropriate secret knock. His device fits easily over the inside of your doorknob and look, uses a computer board known as an Arduino to time the knocks that it senses, to match them up with the secret one it's programmed with. If you don't know the secret knock, the door won't open. It's as simple as that.
Just like some of the doors that are locked with numerical pads, this device is really interesting from a safety point of view, as no one can see that your front door is activated this way. There are no signs pointing to this system. No sensors, no numerical pad, nothing but a smart door that can open itself to the right people. With a long enough secret knock, you simply stop people from being able to open this door randomly, without knowing the code.
What's even more amazing is that Steve made this himself. Check out the video and his post on how he did this exactly.