Forgetting to close your garage door after bringing your car in is a big security risk, allowing people to just wander in without you knowing. This happened a lot to a friend of maker Gareth Loader, so he decided to make a detector to remind him if the garage door is still open.

The receiver
The receiver

Gareth used a simple concept to do the detection - a cheap ultrasonic sensor mounted on the ceiling near the door. When the door is open, it covers the sensor's usual unobstructed view of the floor, and the sensor can detect this massive change in distance. The sensor is wired up to an Arduino Pro Mini, which sends the data into the house via a 433MHz transmitter. Inside the house, in a clearly visible place, another Arduino with a receiver is mounted, and lights an LED if the door is open.

This is an ingenious way of detecting whether the door is open, as there is no need to hook into the garage door’s electronics. This project can be adapted to display the status in different ways. It could be sent to a server, which tracks the status, and sends an email out to the owner if the door is left open.

Gareth is looking at implementing solar power to this project. The detector is currently plugged into the mains using and 9V DC power plug, and the receiver is powered by batteries. If this project could be powered from solar, it would truly be a set-and-forget project.

You can read more about the project on Gareth's blog, which includes the full source code.