Connecting smoke alarm to burglar alarm

[robgraham]

My garage is separate from the house by about 20m. There is currently a bit of a worry about security and I have rigged up a burglar alarm.

It then struck me that it would be a bonus if I could link a smoke alarm into that too. Electronics is my training so I don't have any problems in that area, but I've dismantled the smoke alarm (ie got it out of the plastic !) and am puzzled to see that the piezo sounder has

3 leads - why ?.

The IC is under the sensor cover - would anyone know if that is likely to have a dc output rather than the switching one for the sounder ?

Thanks Rob

[Andrew Gabriel]

Look at this thread:

[Toby]

Another option would be to install a 12v detector like the Menvier m12.

[cj]

Hi There are many smoke alarms out there (as posted) operating on 12v or you can buy a 240v unit with relay from most good diy outlets or if you are near an alarm supplier see if they do an adapter unit . As for the 3 wire to the piezo I can only think it is for the test button as some piezo sounders are dual voltage amd have 3 wires (com ,low,high). HTH CJ

[Andrew Gabriel]

but bear in mind that 12V buglar alarm smoke detectors don't have a sounder built in to them - they rely on the alarm to do that.

[robgraham]

Just to keep this thread going ('bumping' I believe), the smoke alarm in question is a cheapy from BnQ (~=A36) called a Fire Angel. It dismantles quite easily though the labelling on the back needs to be ripped off, and the pc board comes out OK - I then desoldered the ionising device cover and found an IC in there which conveniently comes up on the web (RE46C122). Pin 2 of this is designed for triggering other alarms and goes high when the alarm goes off - isn't that convenient ! There is a track from this pin to the test/hush switch which will make a good output point.

I haven't tried it yet, but this gives me the 'in' that I wanted - assuming that there aren't variations on this IC that don't comply with the data sheet of course !!

Rob

[ARWadsworth]

Did you work out why there are 3 cables to the sounder?