If you work in a lab, the last thing you want is someone barging in when you’re about to complete your latest experiment or build, disturbing all of your hard work. You could use a paper note, or perhaps lock the doors, but if you’d like to inform potential disruptors of what you’re doing and give them a way to signal you, this system looks very useful.

The device, which is installed in a psychology lab’s door, uses an Arduino Uno to display an LED for “Experiment In Progress” or “Clear,” and has a backlit LCD screen below for more explanation. The screen’s backlight powers up via a sonar sensor if someone approaches, and messages can be updated over Bluetooth.

Finally, if you’d like to get the person inside’s attention, it even a doorbell feature that blinks a light and optionally beeps. For more info on the project, check out its creator’s Imgur set or Reddit post.