Sonar for your Home

One of the challenges in creating an intermediate-level smart home is making educated guesses about things that are happening around the house. For example, if you can detect which cars are in the garage you can infer who is home and use this to inform the decisions made by your home automation system. In my case, if both of our cars are gone then its a safe bet the house is empty and the alarm can be set, the heat turned down, and extraneous lights turned off.

James Sentman has a new, interesting solution for detecting the presence of automobiles in his garage using tiny sonar rangefinders from MaxBotix. It's a simple idea, really, but only made possible by the availability of inexpensive ($25) sonic sensors. They work by measuring the distance from the sensor to the nearest object. So, if you mount the sensor on your garage ceiling you can tell if a car is parked underneath it. If you and your housemate consistently park in the same spot, use two sensors and you can guess who is at home based on the presence of their car.

Of course, you need a way to monitor and read the data from the sonar devices. As it turns out, James Sentman is one of the creators of XTension, the venerable program for Mac-based home automation. The next version of XTension (currently in private beta) will have built-in support for these sensors. You can read all the details in Sentman's MaxSonar sensor and XTension article.

I'm eager to try these out, and it seems like there are other interesting ways they might be used. Another example is measuring the salt level in a water softener at the CocoonTech forum. If you have an idea or experience with them, feel free to post a comment.