Hardwired Alarm Sensors & Arduino

I’m trying to find a guide on setting up hardwired door and window contact sensors that are already prewired to a GE alarm in my home. There’s a few threads on it but they are a bit all over the place and I’m not sure where to start.

I came across this ST shared app in the IDE: https://github.com/coolkev/smartthings-alarm

The readme makes it sound pretty simple but I’m looking for more details. Not sure if this is a working app or if anyone is using it.

Ideally I’d like to take an arduino things shield and wire each of my alarm sensors to it. Possible? Any instructions on how?


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Here’s what I’ve been given to work with:

I’ve never used an arduino before so my knowledge of it is limited…

Based on that github link it sounds like I should attach wires from the “COM” screws on this board to ground. Not sure if that means there is a ground on the arduino or they just need to be grounded in general. Then each of the 4 zones should go to ports on the arduino.

So I’m guessing its much easier to send each zone to smartthings rather than every door/window individually. Each sensor by itself would be really nice but at least it would be better to have zones than nothing at all.

@mweston Check out this project, you should be able to use most of the code for the Arduino and Device Type.

The best way I can recommend to do this does not utilize the arduino at all… If you know how to use a soldering iron then buy one SmartSense Multi for each zone and solder 26 awg wire (or one pair out of a CAT-5 cable) to both sides of the magnetic sensor then connect one side to common and the other to each zone trigger. This is much more reliable, bit less effort, and better integration with ST.

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I’ve done the same thing, but with no soldering. The Ecolink/Schlage door/window sensor has internal screw terminals for doing what’s described here, or for using one device on more than one window along with extrenal magnetic contacts. I’ve been able to successfully use these devices for each zone I wanted to move from my Ademco alarm panel to ST.

That said, I am moving zones back to the alarm panel because I have installed EyezOn’s EVL-3 module, and I’m hoping to have integration between that and ST in the future.

@johnconstantelo and @cooperglee are you monitoring your hardwired sensors that are also connected to a live alarm panel? Or have you moved those sensors over to ST.

I’d like to keep my alarm panel operating as it is now, but use ST to monitor a few of the hardwired motion sensors.

@NorCalLights, I want to do exactly what you describe, but for some reason I can’t get ST and my alarm panel to do that. When I add the Ecolink/Schlage contact sensor to the end of the loop (supervised or not) and I trip it or open another window in the loop, only ST sees it opened. No matter what I do the alarm panel never faults. I haven’t tried a motion sensor yet, but I expect the same behavior.

For folks that want to move from their alarm panel to ST and use their existing hardwired sensors, the Ecolink/Schlage devices work nicely; but not if you want both to work together.

Long answer to your question - I had to move hardwired devices to ST and disable the zone in the alarm panel.

Since I didn’t really want to do that, I’ve moved the hardwired sensors back to the panel and hope to integrate the EVL3 to ST in the future. I’m also hoping to understand why using both the alarm panel and the Ecolink sensors won’t work.

@johnconstantelo When I meter my door sensors for contact closure (continuity) in parallel across the Com and Ground terminals on my panel, I do not see a change when the door is opened. However, I do see a voltage change (something like 6V when open and 14V when closed, but I don’t have my notes in front of me). I think, with my setup at least, I might need to monitor for a change in voltage, not contact closure.

FWIW, my panel looks a lot like the photo that @mweston posted.

When I get home tonight, I’m going to experiment with the motion sensors.

I have an extra Schlage contact sensor laying around that I’m going to try to hook up to a zone. It would be really nice to be able to see each individual sensor on ST instead of just zones but I assume that would require some serious rewiring around the house.

Anyone know if the EVL3 works in zones or does it show each sensor? I don’t think I can use the EVL3 with my GE alarm but I’d consider buying a new alarm panel if it could do each sensor.

@mweston it might not be as bad as you think to rewire… my system is wired so each sensor has it’s own cable bundle coming back to the panel’s box, and all of the ganging for zones is done at the box end. Since the panel only has a limited number of zones, it’s common to gang a number of window contacts (for example) in series into one zone. Door sensors and motion sensors are usually wired individually to their own zone.

If you can find out where that ganging is done, it should be easy enough to tap in at that point.

The question remains, however, can we monitor those connections for contact closure, or do we need to watch them for voltage changes.

Yes, monitoring the actual “contact” sensors without impacting the functionality of the alarm system. This is why I did it this way because I did not want to invalidate the insurance discount I get for having the “alarm system” - hard to convince the insurance company that my ST integration has the same capabilities.

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Well, there might be one caveat that you might have with your alarm system - the contacts that I am connecting to the ST Multi are all just “open/closed” sensors with no voltage - any amount of voltage on the line will give false readings and/or short out the ST Multi. If there is voltage on the line it is not a problem - just need to put a properly suited relay on the leads and then connect the ST Multi to the “dry” side of the relay. I have done this on the back side of my Nest for the “Heater” output as I have a microswitch furnace that provides just enough power to keep the ST Multi “always on”. So - the Nest is connected to a double-pole relay that it “thinks” is the heater and then both the ST Multi and the furnace are on separate poles of the relay. I can send pictures and/or wiring diagram if anyone would like.

Usually the zones are all wired as one - if all the wires are “home runs” then you could put relays on the ones you want to specifically identify - it would be easier to just add ST Multis at the locations you want…

Hey Cooper…

I’m interested in the details of your home insurance discount (there is actually a thread on the topic, if you would like to join the conversation…). In short, my insurance company does not seem to offer a substantial discount, but they also don’t have specifications for the minimal discounts they offer.

An easy and “elegant” choice, but seems quite expensive compared to a single Arduino setup that could monitor dozens of contacts…

Either way will work - if they are “dry contact sensors” just wire them in parallel - if they are voltage changing add relay - from experience the ones that have voltage for the sensor usually do one of two things - shunt the wires or drop the voltage. In either case a properly connected relay will work.

Agreed as more expensive and more elegant! Although I am happy to “tinker” on my projects, I personally feel that all Arduino projects are not really “consumer” ready - the building and casing and writing of code I find to be a too much for someone wanting something easy and reliable. My significant other hates my “mad scientist” projects and when not working flawlessly wants my head on a platter. Simple ST devices seem to be more acceptable and reliable…

I think a relay is what I will need. I just tried hooking up a schlage contact sensor to my alarm panel but SmartThings always reports as closed even if the door is open.

My voltmeter readings are showing 6.8 volts with the door closed and 13.5 when open.

I wired the + side of the Schlage terminal (green wire) to the Z1 terminal on my alarm and the - side of the schlage to the COM terminal on the alarm.

Any ideas on what type of relay I will need and where I should place it?

An easy and “elegant” choice, but seems quite expensive compared to a single Arduino setup that could monitor dozens of contacts…

Agreed. I have a total of 14 sensors that I would like to monitor individually and the schlage method is really simple but the arduino way would be much cheaper. I’m not sure how much harder it is to wire an arduino and get it setup on smartthings though, sounds a bit more complicated.

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The first time someone does this type of hardwired sensor to SmartThings via Arduino Shield integration in a “good way” it will be pretty difficult, but I would say not beyond the skills of a “hobbyist”. I would find this to be a fun project, for example, though if I ran into particular quirks on the hardware side or SmartThings limitations, it certainly could get frustrating pretty quickly.

It would be nice to have financial incentive, but there is no formal method in place, just donations offered on popular projects shared here.

On the other hand: I seem to recall that there is a commercial Z-Wave based device specifically designed to integrate to a hardwired contact sensor panel. So that’s a possible route. I wonder if I bookmarked it. Try some aggressive Googling?

…CP (Terry)