Connecting fire alarms to burglar alarm

[Lee Nowell]

Hi All,

We have a burglar alarm with a couple of spare "zones". Unfortunately, when we had our fire alarms fitted (mains powered and all interlinked), I didn't think about integrating them with the burglar alarm so we will be notified if the fire alarm goes off whilst we are out of the house.

I was wondering, if I put a relay in, would I be able to connect the 2 together such that the burglar alarm treats it like any other zone in the house.

My logic (which may well be flawed!) is as follows....

- connect the 240v interconnect from one of the smoke alarms to one side of the relay (I have assumed that the interconnect goes "live" when the fire alarm goes off - is this true or is it a switch?)

- connect the 12v alarm wire to the other side such that the relay opens the switch when it gets 240v the other side (i.e. breaks the alarm feed and sets the alarm off).

I'm sure it is not really this easy ..... and would greatly appreciate any help you folks can give me.

thanks

Lee.

[Tim Watts]

I have a strong feeling that the "interconnect" may be more than a simple on/off signal in many cases and that it will be manufacturer dependent.

Mine (Kidde) can support a manual intervention switch on the interlink that allows testing *and* silencing of all alarms.

There are also warnings of not running the interlink cable closed to dimming circuits which suggests a more complex signal.

The Kidde ones do have an optional extra:

doing what you want.

HTH

Tim

[Andrew Gabriel]

Some interlinked alarms have a relay module which can be connected into the interlink, but these aren't cheap. If there's one available for your model, you could link it to one of the alarm zones.

Mine are the other way around. The smoke detectors run off the burglar alarm. They are standard 9V battery ones, but an alarm interface unit same size and shape as a PP3 battery fits in them, which steps down the 12V alarm supply, and signals back to the alarm panel if they go off. (It detects this by the increased current draw of the smoke alarm siren.) Unfortunately, I haven't seen these available recently - they probably don't conform to current regs anymore.

[ARWadsworth]

You can still get them. Bottom of this page

[Robin]

the unit won't (or might not) see the current draw. But does it work with just one module in one of the interconnected alarms? I can't see why it would not but there's a lot I can't see.

(Not a hypothetical question as I've got interconnected mains powered Kidde smoke/heat alarms and plan to fit a burglar alarm next year.)

[ARWadsworth]

The link was for battery powered alarms not interconnected alarms. That is what I assumed Anderw had fitted.

Now the module at the top of the page may work with interconnected smoke alarms. When I tested the output on an interconnecting wire it went from 0V to 9V DC when the alarm was activated. The link below seems to confirm this.

should be possible to use the 12V module to link interconnected alarms to the burgular alarm.

[Robin]

Sorry, my mistake. I had galloped through from the OP and failed to spot Andrew's reference to standard battery detectors.

Thanks again. I think I might nevertheless try i.d.c. one of the S300 you originally pointed to as the Kidde alarms work on battery as well as mains and it would be a neat way of making the connection. And thanks too to you and Andrew for pointing me to things I never knew existed .

[Andrew Gabriel]

It would not work with a mains/battery alarm.

[ARWadsworth]

I suspect that you were correct when you said that a mains powered smoke alarm with battery backup will not cause the voltage drop needed to activate the S300 device.

Also you would need one S300 for every smoke alarm in your house (the interconnect cable is just a trigger not a supply). However the S320 would only need to be connected to one detector (unless you want the alarm to know which detector was triggered).

Cheers