Anyone who spent any time being a kid can probably remember having a clubhouse, or building forts, or just really wanting a secret hideout. And of course, every secret hideout requires a good secret knock. Well, now that you’re all grown up, you can finally have a door that opens with a secret knock. Steve Hoefer went and cobbled together a few odd bits and pieces from his lab to make this simple but fully functional secret knock-detecting door lock.

He used an Arduino microcontroller, a piezoelectric speaker, a gear reduction motor and a few bits of PVC pipe. He even includes a schematic and the Arduino source code over here if you want to make one yourself. But if you don’t have the technical prowess to put things together and make a functional new thing, don’t worry: Steve is planning to make some kits which you can purchase to make your very own awesome secret door knock lock.