SmartThings Community

Smart smoke alarms with dumb smoke alarms (EU/Ireland)


(Raghuvir Gupta) #21

Having a smoke alarm at home is a wise decision to make. I have adorned my smart home with the best smoke detector from Nest. It is competent to recognize smoke as well as carbon monoxide. You must check it out once.


It is mandatory in the US and I think it is now in EU as well, more than a wise decision, it is a life saver.


I would not make any assumptions that something that is either possible or legal in the US with regard to either wiring or smoke alarms will also be legal/possible in the UK.

UK does not assume that most electrical work can be done on a DIY basis the way the US does.

There are relay devices With a similar function, but you can’t use the one that was linked to and meet UK safety codes.

Instead, you have to buy smoke sensors which are designed to have the ability to have a relay added, And there will be a relay piece specifically for the purpose of connecting to external systems, and it will generally slot into the smoke sensor itself, not into the mains.

Here is just one typical example:

There are lots of these, so you just have to check the specific brand and model of smoke sensor you are interested in.

Community members from the US should be aware that these kinds of issues come up frequently in the UK discussions, so please only recommend specific devices if you have verified that they meet code in the UK. :sunglasses:


I was born and raised in Europe, everybody does DYI projects to great extent just like in the US. Some bother with code some don’t (most don’t from my personal experience), many hire pros “under the table” to avoid paying taxes, probably more than in the US. Adding a relay to an existing smoke alarm system should not bring any concern, especially this particular relay which is specifically designed to be used within a smoke alarm network normally used to hook up an alarm pull, strobe or sirens. Obviously actual models available in the UK or in Europe generally speaking may differ but the principles are the same.

(Travis) #25

Do you know if you can use the other leads from the kiddie accessory to a zwave switch to trigger the smoke detectors audio alarm contact to make the smoke alarms siren for instance if there was an intruder.


That would be a cool hack.
These specific fire alarm relays are usually used to manually trigger an alarm, for example using a pull down alarm trigger. I am not sure if they trigger the detectors to sound or if that requires wiring an external alarm to it.
I suggest you find the user manual of the relay, Kiddie or other makes and go through it. I remember there was a wiring diagram on how to wire these external triggers, also you can wire a strobe or external siren but I don’t know about triggering the detectors, If not you could try adding a bypass into the red wire. The red wire is what triggers the detectors and it sends 9 volts I believe. If you could send the 9 volts into the circuit from another trigger, it might work (probably would not be legal however).


Unfortunately , I found this post too late, it appears that the Aeon Labs ZW097 Dry Contact Sensor is not available for sale anywhere. I am looking for an alternative do you think this would work?


They told me back then that it was not a big seller and there was a chance they would discontinue it, I’ve bought a couple in advance. Any dry contact you can find will do or you can also use a door contact and short circuit the magnetic contact… solder a small wire between the two poles.


Bummer! I guess I can try that one , I can’t really find any other dry contact zwave on the market and I am not sure I can short circuit the door contact.


Sure you can.
See on that picture for example the glass part on the right between the two copper wires (on the top, not the LED) is what activates the door contact with the magnet.
So all you have to do is solder a wire on each side bypassing the glass part. You can cut it out or leave it, does not matter.

The rest is identical with the dry contact, the dry contact was just a door contact without the magnetic switch.

(Robin) #31

There’s loads of zwave dry contact devices out there… it’s just that they don’t always call them that.

Normally they are advertised as door / winnow contact sensors and when you read the specs many of them have the option for wiring in external sensors (dry contacts).

You really shouldn’t need to break out the soldering iron, though that option would of course work if it came to it.


I ordered the other one before seeing the post about dry contacts. Will rig it up and see how it works.

I have to say , I am not on the smarthings platform , I am a Vera user, but you guys have been most helpful! Maybe I should look at switching hubs.


Finally got the items for this project. I am struggling with determining what T1 and T2 is on my dry contact sensor . This is what it looks like.

(Robin) #34

L & N are your mains supply

Relay (load) is for an output (probably not required for your use-case)… this output would toggle in sync with the dry contact.

The two terminals on the right are the input wires coming from your smoke alarm.


Just to make sure I understand correctly. I have to power the dry contact using L&N.
I use the blue and orange from the SM120X to connect the 2 slots on the right of dry contact
I also connect the Black , red , white, on the SM12x to the smoke alarm

Does that sound right ?


It seems L stands for “load” and N for “neutral”. Read the manual, does your contact need to be powered? The dry contact does not require any power (other than the internal battery), basically T1 and T2 is a closed switch which when triggered by the relay it opens.

The switch (so same as T1 and T2) seems to be the two on the right since there is a switch diagram on it but it shows open, which is fine too, it would then trigger when closed so in ST it should show “open” while the door contact would show “closed”. Works the same but the smart app would be opposite (send SMS when closed instead of when open). If that was not working then you may need to use the NC (normally closed) wire of the relay instead of the orange one. To test it just press the smoke detector button.

The relay load I think will power something attached to it when the switch is closed so you could for example turn on lights if you had a light bulb powered through that “relay load” circuit, otherwise it’s of no use for that application.

I don’t remember, check the output of the relay but I think it’s only 9 or 12 volts so you would need to power the switch from the main circuit and not the relay.

If you lose power that switch won’t work as opposed to a dry or door contact as these are self powered (and assuming your internet and ST are on battery back up). The smoke detectors do work on battery when you lose power, that’s why the red wire is 9 volts, which is the battery output.


It appears that the dry contact does indeed need to be powered to work . I don’t want to deal with another high powered device I would need to hide in the wall so I am going to look for another dry contact that is battery powered or use a door sensor like you suggested .


I think also it would be better with a self powered device. Just stay away from the Samsung door contacts because they are super small and you may have a hard time jumping the magnetic switch and mine stopped working after a few months.

Something like this should work fine

(Robin) #39

You don’t need to mess with the circuitry in the above example… the wired inputs are in parallel to the reed switch… jumping the read switch would just force the sensor to constantly report closed.


Good point, so instead of using the orange wire, he may need to use the other one that’s for NC (normally closed), don’t know what color it is but it says on the relay.