Hacking a hotel door

I hack a door to open itself when you throw gang signs at it

I’m living at a hacker hotel in Finland building stuff for the next 2 months (shout out https://fr8manifes.to).

While the room is big here and the working space is hecka cool, the biggest problem is actually with the door.

Since I came here, I’ve been locked out of this room at least 5 times, simply because I forgot the keys inside. So I thought why not make this boring door into a magical one, one that you can open with hand gestures.

Building a cool door

The door we have is like any door, with a peep hole and a lock. It would be very simple to just change the lock, but there are a few constraints, I can’t drill holes and pull anything out. So I have to think of creative way to put stuff on top of it.

Since we want to throw signs at the door, we need to do hand pose recognition. For this, mediapipe is the obvious choice to go, it’s a simple library that you can setup on any device. With this, you can get the hand pose of any image. However, instead of using gestures which is very unreliable sometimes, I’m going to count numbers of fingers up.

This makes it expand automatically to various hand poses while making the whole system simple to implement.

To have this on the door, I just design a 3D enclosure, slap a webcam and some leds for feedback, then hook all of them to a pi 5 behind. You can say this is pretty overkill, but either way I’m running some stuff on the pi, it doesn’t matter where it is.

For the door to open itself, well, this is lucky. I built a self balancing robot with nema 17 not long ago, so I still have the board for controls laying around.

I just designed a bevel gear set with a 1:5 ratio to put more torque on the door, and voila it just works. The motor will run 50 steps if I send a on command through the serial interface of this esp32 from seeed studio.

If I send an off command, the motor will be disabled, having minimum power and heat dissipation. This allows me to open the door from the inside or with a key from the outside.

Combine all of this, I have a very cool door that opens on gestures.

A surprise

But, it’s soon become something I didn’t expect. As soon as I put this door up, at least 3 people have been able to bruteforce and come into my room.

It’s become a challenge to crack the door.

So the natural next step is to add 2FA, so the door only recognizes the password given by me and not others.