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I bought a 4 level house that had an ADT security system with a motion sensor in every room. I never used it since moving in.

But I have a fun project in mind: I'd like to drive my kids nuts when playing hide-and-seek.

Is there a relatively easy and inexpensive solution to reusing the motion sensors. It would be sufficient to have an app (or a webapp) that gives me a flat list of the most recent motion-detector "hits". Any suggestions?

  • Probably not. If it is an older system, the dumb sensors will only trigger a phone call to the monitoring company. If it is a newer system, you will need a subscription to access it via the internet. – Mattman944 Oct 23 '19 at 0:19
  • if the sensor is wired, then it is posible that the sensor acts as a switch .... check to see if wires are getting shorted together when motion is detected – jsotola Oct 23 '19 at 0:43
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    You realize this is not a simple project, and will involvee a buch of cross discipline work. The hardware build alone will be considerable, and then it has to talk to the Internet somehow, a piece of engineering of its own. An engineering firm might bill it at $100k, or a kid might do it for 2 months of evenings if slipping grades were no object... – Harper - Reinstate Monica Oct 23 '19 at 1:11
  • Raspberry pi to monitor the sensors, and talk to a website on the internet (or use your home computer) of course you need to write some software and program the pi... Would be a very cool project, not to hard either if you can code :-) I would of course do this in assembly – Gunner Oct 23 '19 at 2:06
  • are they already powered on? if so, that makes it trivial to monitor the feedback line, which will go high/low depending on activity. I would suggest have a time-based indication instead of a state indicator, maybe fading the alert away. That lets you see where the last activity occurred, were the kid staying still while you search. – dandavis Oct 23 '19 at 16:37
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First we must determine whether your motion sensors are wired or wireless.

Wired

The wired PIR motion sensors used in security systems since roughly forever are pretty simple devices. You feed them 12 volts dc to power the electronics; they contain a relay which opens or closes to indicate motion. Some will have a SPDT relay so that the installer can choose whether to use the normally open or normally closed contact. "Normally" means the inactive or resting state of the device, ie no motion detected.

If your ADT system is wired there'll be a control panel buried in a closet or utility room somewhere in the house. Open it up and you'd most likely find a 4-conductor cable for each motion sensor. If the motion sensors are grouped into zones then it's possible you'd have one cable for each zone; each sensor might not have its own "home run" cable back to the panel.

All these wired sensors could be fed into some kind of multi-input interface. That might be built around an Arduino, a Raspberry Pi, or some other experimenter/hobbyist platform.

Wireless

If your motion sensors are wireless then things aren't necessarily harder, just different. First you'll have to figure out what RF frequency and protocol they use. At very least they should be labelled with an FCC ID number which reveals the manufacturer and model of the device, and from there the rest can be discovered. They might also simply be labelled such that a person familiar with the industry would recognize them. GE/Interlogix is one particular make that's quite prolific. Each sensor has a unique serial number which it periodically transmits along with its battery state, contact state, and other info. Receivers are available that can listen for these sensor transmissions and send it over a serial bus like RS-232.

Pulling it together

Identifying what sort of sensors you're working with is the easy part. From here you're probably going to be looking for some kind of open source home automation platform such as openHAB, Home Assistant, etc. These may provide a software framework for receiving the security sensor inputs and putting them into a web or mobile app front end you can use. This all goes beyond the scope of the DIY stack exchange, but hopefully I've given enough ideas and key words to help your research get started.

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