The Garage Door Minder

I’m glad we live in a low crime area: I have a tendency to leave our garage door open, sometimes all night. I have even considered installing a warning light over our bed to make sure that doesn’t happen. Instead we have tried to be more disciplined, but we’re not perfect. My wife recently asked if there is some way to have our garage door alert us when it is left open.

A few months ago, I designed and built an interface that allows authorized users to open and close our garage door with a web application that uses OneID identity management technology. Part of that interface, although not shown in the YouTube video, allows the user to see whether the door is currently open or closed, so they can be sure what’s happening if they want to operate it remotely. Given that this is done with a Raspberry Pi processor running Linux that has access to the state of the garage door, it should be a simple matter to monitor the door and generate alerts. And it is.

The monitoring of the door is very straightforward. The socket interface provided by the Raspberry GPIO Daemon easily supports multiple clients, so long as none of them keeps their socket connection to the daemon open except when they’re actually using it. So it was just a matter of writing another daemon (background process) that wakes up periodically, checks the state of the door, and generates an alert if some criteria have been met.

I considered a couple of different ways of alerting. The most straightforward seemed to be to send a text message to each of our cell phones. This can be done by sending an email to the appropriate email address provided by the mobile carrier, but this seemed susceptible delivery delays and has many dependencies on intermediaries that could interfere with its reliability. Instead, I tried using Twilio, a provider of an API that allows one to send and receive text messages and phone calls. Sending text messages in this way costs very little, and seems to provide very prompt delivery.

Both my wife and I receive the notifications, so it made sense to generate a second notification when the door is closed following a “door left open” alert. This saves a lot of “did you get the door?” messages between us. We have the monitor set to alert after the door has been open for an hour, and it has already been helpful.

The code for the Garage Door Minder is straightforward, but needs some work before it will be ready to post to GitHub. If there is sufficient interest, I’ll clean it up and get that done.

There are lots of useful control and notification alert applications for internet-connected devices (the so-called Internet of Things) in the home. Here’s a modest example.