Ben Brooks' Secret Bookshelf Doorway Hides an Unusual Secret: It's Automated with ESPHome

Mechanical engineer Ben Brooks has created a secret entrance worthy of any haunted mansion — but tied into a Home Assistant home automation system via ESPHome, making it possibly the most convenient hidden bookcase door in history.

"I’ve had my office/workshop in a basement nook (next to the laundry room, of course) for quite a while but have always just had a cheap vinyl door to separate my space from the chaos of kiddos," Brooks explains. "While I've considered putting in an actual door in the past, the fact that it wasn't NECESSARY and that it isn't a standard size meant that I was going to end up spending more than I'd like for something that would still look kind of off."

Rather than a plain door, then, Brooks decided the money could be put to better use building a classic: a bookcase which swings out to reveal a hidden entrance. Building the bookcase himself, from 2×10s and plywood, with the lumber coming in cheaper than the cost of an actual door. Hinges good for the total weight countersunk into the door frame provide a means for the shelves to open and close — but what the doorway really needed was a locking system.

"For the locking mechanism, I started off with a small and cheap solenoid door latch I had leftover from a previous project," Brooks explains, but that turned out to be unreliable. "After a little research, I landed on a magnetic lock (like those used for security doors) and found one on Amazon for a reasonable price. After waiting for it to arrive and then testing it out, it worked like a treat! It claimed to be rated for 160lbs of force, and while I didn’t test this to its limit, it's never unlocked even with some fairly firm pushing on the door."

A counterweight system, craftily constructed from hooks, a rope, and a dumbbell weight, allows the door to swing open automatically when the magnetic latch is released. An Espressif ES8266 controls everything, using the ESPHome firmware — listening out for the movement of a reed switch connected to a secret book trigger and unlocking the door when the right book is chosen. "All of the automation to make the door work is done locally on the ESP device, but obviously I still have the possibility of integrating it into the rest of my home automation setup.

"As a final bit of fun, I realized I should really add some audio effects to the process of opening it up. I already had a 'smart' speaker in my office for listening to music, and with Home Assistant it's trivial to make an automation to play something upon unlocking the door. After some brainstorming, it was obvious I needed to use some audio from Young Frankenstein (or is that Fronkensteen?). 15 minutes of downloading a handful of fitting clips and I setup an automation to play a random one upon unlocking the door."

Brooks' full write-up is available on the project's Hackaday.io page.