Over-engineering Ding Dong Ditch

One day, [Samy]’s best friend [Matt] mentioned he had a wireless doorbell. Astonishing. Even more amazing is the fact that anyone can buy a software defined radio for $20, a small radio module from eBay for $4, and a GSM breakout board for $40. Connect these pieces together, and you have a device that can ring [Matt]’s doorbell from anywhere on the planet. Yes, it’s the ultimate over-engineered ding dong ditch, and a great example of how far you can take practical jokes if you know which end of a soldering iron to pick up.

Simply knowing [Matt] has a wireless doorbell is not enough; [Samy] needed to know the frequency, the modulation scheme, and what the doorbell was sending. Some of this information can be found by looking up the FCC ID, but [Samy] found a better way. When [Matt] was out of his house, [Samy] simply rang the doorbell a bunch of times while looking at the waterfall plot with an RTL-SDR TV tuner. There are a few common frequencies tiny, cheap remote controls will commonly use – 315 MHz, 433 MHz, and 900 MHz. Eventually, [Samy] found the frequency the doorbell was transmitting at – 433.8 MHz.

After capturing the radio signal from the doorbell, [Samy] looked at the audio waveform in Audacity. It looked like this doorbell used On-Off Keying, or just turning the radio on for a binary ‘1’ and off for a binary ‘0’. In Audacity, everything the doorbell transmits becomes crystal clear, and with a $4 434 MHz transmitter from SparkFun, [Samy] can replicate the output of the doorbell.

For the rest of the build, [Samy] is using a mini GSM cellular breakout board from Adafruit. This module listens for any text message containing the word ‘doorbell’ and sends a signal to an Arduino. The Arduino then sends out the doorbell code with the transmitter. It’s evil, and extraordinarily over-engineered.

Right now, the ding dong ditch project is set up somewhere across the street from [Matt]’s house. The device reportedly works great, and hopefully hasn’t been abused too much. Video below.

20 thoughts on “Over-engineering Ding Dong Ditch

  1. I reverse engineered few similar things for friends. Those guys who make garage doors charge about 50$ for remote, I use SDR (or small 433MHz receiver module + Saleae) to figure out the protocol and then I can make new remote for about 5$. Problem is that new systems have rolling code so you can’t simply clone the remote.

  2. *Wonderful* general tutorial on waveform hacking etc. – I may have to start tinkering with SDR.

    Two trivial whiny comments:
    The FONA board is ~$40 by itself though, so you’re going to spend a bit more than you think.
    I wish he’d get a microphone separate from his laptop so you don’t hear every keystroke/fan noise.

  3. Went to visit my friend on day and realized he didn’t have a doorbell anymore (this was before the days you called you friends to see what they were doing before going to their house). Turns out his wireless doorbell rang the house across the street. So much fun watching the neighbors look out there door and yelling down the street at random people.You would be surprised how many times you can get the same person to come to the door in the span of 5 minutes.

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