Guessed by Paragliding_Dave

It detects your knock on the door, and counts up how many. The headphones are for telling you when to start knocking, start knocking when it's not beeping to confuse onlookers
 
 

Enigmaker would not be possible without...

If you would like to work with me on any of these projects, turn them into products, or just build your own, then get in touch.