Picture of Home Alert: Arduino + Cloud Messaging On A Large Display

In the age of mobile phones, you would expect that people would be responsive to your call 24/7.

Or… not. Once my wife gets home, the phone stays buried in her hand bag, or its battery is flat. We don’t have a land line. Calling or SMSing to ask for a lift home from the train station on a rainy night or calling to ask if my keys are still on my desk is literally wishful thinking.

I have this problem often enough to warrant a solution. A bit of tinkering with an Arduino and a Freetronics Dot Matrix Display (DMD) resulted to a very annoying (for my wife) gadget, but an amazing communication device and information center for me. I love it, and it’s only version 1!

Home Alert is made of these parts:


  • A Freetronics Dot Matrix Display, which is an array of 16x32 LEDs. They come in different colours, but I use red to emphasise that this gadget is for “critical” notifications.
  • An Arduino Uno with an Ethernet Shield.
  • A real-time clock breakout, like this or this.
  • A piezo buzzer
  • A DHT22 temperature and humidity sensor.


Home Alert is controlled via a web page that is hosted on Heroku, a cloud-based application host. The web page is coded in Ruby, using the Sinatra web app framework, and the Redis key-value store.

Have a look at the home page (show in the first attached image in this step), where the form awaits a new message from the user.

The first field accepts a numerical hardware code. It’s a code that allows you to target a specific Home Alert system, as each can be given a unique code. Or, you can have multiple Home Alerts sharing the same code, so that the same message is displayed to multiple locations.

The message you want to display goes to the second field. Any text you type in there will be displayed in the DMD.

If you want to make some noise, check the Yes! checkbox, and the buzzer is sure to gain the attention of anyone nearby.

In this article, I’ll show you how to build your own Home Alert system, both Arduino hardware and software, as well as the Sinatra mini web application.

Let’s get started!


If you can make it auto update, you can have a universe death clock

Wow Really very useful information.

Thanks a lot for sharing it with us. I will look forward to read more from you.

Could I share this information on my site.

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Hi, thank you for your message!

Sure, feel free to add a link to this article in your web site. It is probably not appropriate to copy the text though. What do you think?

Taerzik1 year ago

This is a really good idea. It could use some fleshing out to make it a final product but I don't really know what to suggest. Maybe a multicolor LED panel using the colors for different purposes like weather alerts, message priority levels, etc.

This is a great idea! Thanks for sharing!