Smoke detector help - electrical question

The house we are buying has 3 smoke detectors in it, one on each floor and they are all hard wired in series with each other.  When I was there with the home inspector, two of the three beeped very quietly when the test button was pressed.  The other one was load as it should be.  Any thoughts?  Bad detector? Bad back up battery? Wiring issue?

Thanks in advance to my bottomless pit of clan knowledge. 

I'm not an electrician but pretend to be one on weekends.. jk... I've done several house wiring jobs and breaker installs.

The only thing that should be in series in house wiring should be a switch and a load (bulb, fan, etc.).
Loads (bulbs, fans, smoke detectors) should all be in parallel. 

This means the smoke detector supply wire (red or black) should be connected to the black house wire (hot) - this goes for all detectors.

The detector ground/return wire should be connected to the white house wire (neutral) - this goes for all detectors.

Hope this helps.. how did you determine the 3 detectors were connected in series?

Wait... you trust US more than Google!? 



You're nuts

Sorry Andy, what I meant is that they all do have the hot/common wired normally and the red wire is in series so when one goes off, they all go off.

LOL when Google comes back with some shmuck on Yahoo Answers, yes I do.

Hardwired smoke alarms should be wired in series, this way when one goes off the rest will.
Non hardwired smoke alarms give a faint beep when battery is failing, so maybe same for
hardwired ones.

Where did i get this information    GOOGLE 

Wiring sounds all right.. the red signal/interconnect wire should be fine because all respond at the same time.

If two sound quiet there may be something wrong with those two detectors.. but could be a sound/tone thing. Detectors are loud high pitched.. how can you tell two are quiet when all are going off at same time? Maybe they're all working fine, just all at slightly different pitches.

You could unplug the 'loud' one and test the two quiet ones, even one at a time to determine if they are truly faulty or quiet. As long as there is a loud piercing sound in all parts of your house and all 3 test buttons set them off you're probably all right.

When you hit the test button, only that on detector would sound.  I did read that detectors should be replaced every 10 years and this house was built in 95 so maybe they are on the way out.

if some are too quiet you (and inspector) can tell owners they are too quiet, over 15 years old and raise doubts about their functionality. Request the hardwired detectors be upgraded (to new hardwired detectors) for safety. It's a small price to pay for a house sale.

no gun...he's just THAT lazy


on topic - when the test button is pressed on one hard wired device ALL devices should sound off at similar loudness

i would just start by swapping the loud one with the faint one and see if it's still loud if so you can rule out any wiring and just replace the detector(s) and/or batteries

our system will test loud even if batteries are not present...the batteries are only there so the detector works when the power is out...ive never seen it affect the function when they're powered by home current

Maybe the third smoke detector is suffering from LAG?

Give it a minutes.. it will go off eventually... during the ensuing fire... 

BlackDeath wrote:

no gun...he's just THAT lazy


on topic - when the test button is pressed on one hard wired device ALL devices should sound off at similar loudness

i would just start by swapping the loud one with the faint one and see if it's still loud if so you can rule out any wiring and just replace the detector(s) and/or batteries

our system will test loud even if batteries are not present...the batteries are only there so the detector works when the power is out...ive never seen it affect the function when they're powered by home current

This is my experience on the apartment buildings we do. And you know they work because all 20-30 apartments on a floor or in a building will sound and its deafening.