Always forget to shut the garage door? This simple DIY solution can help.

Many of us, whether we like to admit it or not, can be quite forgetful when it comes to the most mundane tasks — this includes things as simple as closing the garage door. Similarly, Gareth Loader had a friend who also frequently neglected to shut his overhead door upon entering his house. And with that in mind, the Maker decided to curb this problem by creating a device that would let his pal know whether or not it was left open.

With a little research, Loader tasked an Arduino Pro Mini (ATmega328) along with a cheap ultrasonic sensor to do the trick. These electronics are mounted to the ceiling, with the sensor directed downward at the floor. That way, when the door is open, the sensor outputs a shorter distance measurement than when closed. If blocked, a wireless signal is sent via a 433mhz transmitter to another unit inside the house, which consists of another Arduino, a 433mhz receiver, a LiPo battery and a 5V solar panel. This will flash an LED indicator reminding the user to hit the simple button inside garage.

“The detector has a red LED which lights up when something is within 65cm of the SR04 sensor, and a white LED which lights up when nothing is blocking the sensor,” Loader explains.

Sound like a simple solution to a common problem in your household? The Maker has made his code and sketches for both units available here.