Knocking Box

The Knocking Box is a fiendishly difficult puzzle box with some electronics and mechanical elements hidden inside, designed to be given as a gift. The puzzle box element is actually pretty simple, it just gives few clues as to how it is to be opened (and most of those are misleading). Eventually the recipient gives up. But, then again, that’s the idea, the box wants you to give up. It wants to be put on a shelf and forgotten.

Because, once it has been left untouched for a period of 7 days (as reported by onboard accelerometers) the two hidden features are activated (and stay activated).

1. Echo Knock. The Knocking Box will listen with its onboard microphones for any sound that matches its exterior being tapped or knocked upon. It will count the number of taps or knocks and will knock back the same number of times... with two exceptions. Firstly, if it detects that you have knocked in the tempo of shave-and-a-haircut it will knock back twice to the tempo of two-bits. Secondly, if you knock to the tempo of the drumbeat from the title music from The Terminator, it will knock back between one and five times to indicate battery level.

2. Fingernail scatch. Once the hidden features have been activated and the Knocking Box has in addition not been moved in the last day, it will, at random times (just a few times a day), gently scratch at the inside of the box, as if something with sharp fingernails or claws is waking up and testing its environment.

Internally the Knocking Box is a low power computer capable of working in a sealed environment (something like a Raspberry Pi) with a really big rechargeable battery (so that this can run for months), a servo controller, two quiet servo motors (scratch and knock) with appropriate mechanics so that the rotation of the servos is translated into realistic sounding knocks and scratches. It also includes a microphone and accelerometer (for obvious reasons). Included in the pack (but not intended to be given to the recipient) is a spare battery so that the kind friend/prankster can easily open the box and swap the battery out every couple of months with a freshly charged one while the recipient/victim is out of the room for five minutes. Also included are the instructions to open the box and the magnet that you have to touch to one of its surfaces to release the latch. Software is fairly simple with the exception of being able to understand the sound of a knock be able to differentiate this from other background/handling noises. I’m just going to wave my arms and say ‘pattern recognition’ and ‘machine learning’ for that one.

The Knocking Box is not available anywhere and will definitely not explode in your face. Ever.