DIY ESP32 Alarm System Leverages 433 MHz Sensors

There’s a huge market for 433 MHz alarm system hardware out there, from PIR motion detectors to door and window sensors. If you want to put them to work, all you need is a receiver, a network-enabled microcontroller, and some code. In his latest video, [Aaron Christophel] shows how easy it can be.

In essence, you connect a common 433 MHz receiver module to an ESP32 or ESP8266 microcontroller, and have it wait until a specific device squawks out. From there, the code on the ESP can fire off using whatever API works for your purposes. In this case [Aaron] is using the Telegram API to send out messages that will pop up with a notification on his phone when a door or window is opened. But you could just as easily use something like MQTT, or if you want to go old-school, have it toggle a relay hooked up to a loud siren.

Even if you aren’t looking to make your own makeshift alarm system, the code and video after the break are a great example to follow if you want to get started with 433 MHz hardware. Specifically, [Aaron] walks the viewer through the process of scanning for new 433 MHz devices and adding their unique IDs to the list the code will listen out for. If you ever wondered how quickly you could get up and running with this stuff, now you’ve got your answer.

In the past we’ve seen the Raspberry Pi fill in as an RF to WiFi gateway for these type of sensors, as well as projects that pulled them all together into a complete home automation system on the cheap.

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Stupid Security In A Security System


[Yaehob]’s parents have a security system in their house, and when they wanted to make a few changes to their alarm rules – not arming the bathroom at night – an installer would come out, plug a box into the main panel, press a few buttons, and charge 150 €. Horrified at the aspect of spending that much money to flip a few bits, [yaehob] set out to get around the homeowner lockout on the alarm system, and found security where he wasn’t expecting.

Opening the main panel for the alarm system, [yaehob] was greeted with a screeching noise. This was the obvious in retrospect tamper-evident seal on the alarm box, easily silenced by entering a code on the keypad. The alarm, however, would not arm anymore, making the task of getting ‘installer-level’ access on the alarm system a top priority.

After finding a DE-9 serial port on the main board, [yaehob] went to the manufacturer’s website thinking he could download some software. The website does have the software available, but only for authorized distributors, installers, and resellers. You can register as one, though, and no, there is no verification the person filling out a web form is actually a distributor, installer, or reseller.dist

Looking at the installer and accompanying documentation, [yaehob] could see everything, but could not modify anything. To do that would require the installer password, which, according to the documentation was between four and six characters. The system also responded quickly, so brute force was obviously the answer here.

After writing up a quick script to go through all the possible passwords, [yaehob] started plugging numbers into the controller board. Coming back a bit later, he noticed something familiar about what was returned when the system finally let him in. A quick peek at where his brute force app confirmed his suspicions; the installer’s code was his postal code.

From the installer’s point of view, this somewhat makes sense. Any tech driving out to punch a few numbers into a computer and charge $200 will always know the postal code of where he’s driving to. From a security standpoint, holy crap this is bad.

Now that [yaehob]’s parents are out from under the thumb of the alarm installer, he’s also tacked on a little bit of security of his own; the installer’s code won’t work anymore. It’s now changed to the house number.