Tuesday, 4 July 2017

Techie: How would I do it?

One of the things with the hacking I am doing on this alarm panel is the fact that the messaging is more sort of state based, and means keep sending the same message in case it did not arrive. No sequence numbers or acknowledgments or such.

To be fair, it is not that bad - you poll (and send some message) and expect a response - so not getting one is a clue. But it is not ideal.

Now, the max readers. They have a number of outputs, being 7 LEDs, a beeping noisy thing, and the door release relay. They have a number of inputs such as door exit switch and door open sensor and tamper sensor.

If I was making a simple system to work on a state basis I would report a single status that covered all of those inputs and outputs. I would have a simple message that controlled all of those outputs.

Technically there is one extra input which could be added which is 4 bytes BCD code of nearby key fob code - present or not...

Now, that means you could keep sending the command to set the outputs until you see the status showing the outputs are what you expect.

It means that if something else sent a command to impact the output, like me hacking, or the device reset, or any circumstance where the outputs are not what is expected, you simple send the message to set the outputs as wanted.

This is a simple system.

It means tamper is just an input not a different damn message!
It means you cannot get stuck bleeping forever.

It is not what Honeywell / Galaxy do. Oh well. "legacy"

4 comments:

  1. My alarm broke and I was astounded what they charge even to service them. I replaced the electronics with an arduino, kept the psu and battery backup and now I have a programmable alarm with way more inputs for less that the repair cost of the old one. It's a set of make/break switches, not rocket science. Even the keypad is just a standard 3wire.

    As far as I can tell you can't even buy alarms with the level of funcionality I put in (things like remote arming, remote movement detection, linking with nest to take them out of away mode if someone is in the house).

    I'm surprised the chinese haven't jumped on the chance to make cheap systems.

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    1. Indeed, some of the integration options you have clearly done are exactly what we are looking at. Simple things like if I alarm my man cave, I want the PIRs turned off from 03:00 to 03:30 for the roomba to do its thing, but the door sensors left on in case anyone breaks in. Just daft things like that.

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    2. Oh, and things like "unless my key fob is used, text me if anyone goes in the man cave in the middle of the night even when alarm not set"...

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  2. Check out the pyronix euro, I have one at home. Great kit and not too expensive. I even got the fob to open my garage door as it has a load of relays.

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