question about interconnected smoke detectors

Hi, I have noticed in newer homes that they have smoke detectors that take both a battery and are plugged in to the AC. I think the wires running between them seem to have an additional conductor and if one smoke detector goes off and starts beeping, shortly thereafter, the other ones start beeping as well. How does this work? If you were to mix and match between different smoke detector vendors (all having the interconnect feature, of course), would they all work the same? Is this an industry standard connection? I assume it is an additional conductor that either gets shorted to ground or hot by the tripped smoke detector and when the other ones detect that short to ground/hot, they start beeping as well.
Does any company make something that could tap in to that extra wire so that, say, if I wanted to turn on emergency lighting or something like that, it could trip a relay to do that? I'm thinking something that wires in like a door bell transformer where the line voltage AC is all in the box and the relay contact screws are outside where they belong, not sharing a box with the line voltage at all.
Of course, if company XYZcorp makes an "interconnect smoke detector relay module" that is UL etc approved and can be legally connected to the smoke detector wiring harness in a standard single gang box and will trip a NO/NC relay when the detectors are beeping, I'd like to know about that.
Since IMO, smoke detectors are life safety, I'm not thinking about modifying anything or experimenting on my own. It is more just a curiosity on how the thing works and if there is an industry standard or not. I am sure some of you have modified smoke detectors to do something like this, but I would prefer if these mods were kept out of this thread since I think there are many that feel this is no problem and there are many that feel that modifying a smoke detector is a dangerous thing to do. I, personally, would rather not be lead away in handcuffs after explaining to the fire investigator the cool mod I did to my smoke detectors that caused them not to work when I needed them most and, golly, I don't see why it didn't work right, should I get a lawyer now? the circuit really should have worked....
Thanks
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autonut843 wrote:

You would think that they would make an industry standard for that sort of thing, but unfortunately, not only is there no industry standard, the interconnect specs are different between different smoke detector models from the same manufacturer. There are low voltage interconnects, and line voltage interconnects. And ther eare different standards for the low voltage interconnects. I wired up 9 smoke alarms with interconnects in our house, went and bought 1 hardwired detector w/ battery backup for each floor of the house, and the remaining ones were hardwired models without battery backup. (I figured that one battery backup per floor was sufficient.) Well, after installing everything and testing it, I discovered that the battery backup ones will only remotely sound the other battery backup ones, and the no-battery-backup ones will sound other no-battery-backup ones. After reading the fine print buried in the instructions, it does in fact say that you have to have the exact same model for the interconnect to work. Oh well. I assume that there is some modulated signal that is sent over the interconnect line as opposed to a simple high/low voltage to signal the other units, although this is just speculation on my part, and I've never tested it out. (I'd have to borrow an oscilloscope from work if I wanted to try out that theory.)
Ken
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There are relay modules made for smoke detectors. I used to have one interrupt the power to my oil burner if the alarm went off. I would look at the website of your particular smoke detector manufacturer

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What you want is available and in production. Just not on the low end interconnected ones.
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Once again, I should have Googled first and I would have found my answer. The Firex manual for one of their interconnected smoke detectors says...

So, I think that explains why I haven't found a commercially available relay module to do what I was looking for.
Does anybody have a good idea for a passive way to monitor if the smoke detector is going off? I guess I'm thinking something like a sound pressure level sensor or something like that. Obviously it wouldn't be foolproof. Any other ideas?
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autonut843 wrote:

You can buy smoke detectors that provide dry contact closure on activation. They are available in interconnected models but they are not cheap. If you want smoke detectors that can be reliably monitored from a remote location you should install a listed automatic fire detection system. Since that is work I have done as an electrician I can assure you that it would be both cheaper and more reliable then anything you would jury rig. Systems are available that are wireless. Those systems meet the requirements for interconnected detectors.
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Tom Horne

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wrote:

The only other idea I have is what you said you didn't want to do, but after some hesistation, I did it.
I have, the house came with 110 volt smoke detector in the hall outside my bedroom. In parallel with the noisemaker thing inside the detector, I put a relay that connects to my burglar alarm which sounds a constant noise, not the pulsating noise that breaking into the house causes. I used a fairly large relay but it was still small enough to stuff into the original hole in the ceiling.
It says on the smoke detector not to fiddle with it, of course, but my relay uses less than the noisemaker, and the it's all 110 volts so it's not going to overdraw from a battery. I've tested it more than once. Although it is so loud that I only do it in the middle of a weekday when my neighbors mostly aren't home.
When I sell the house, I'll give them notes about everything I've done to it.
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Thanks for the input.
One thing your realtor may request. Instead of the notes, just swap out the modified smoke detector with the correct one so nothing has to be declared. It'll make the sale go easier. You really don't want to mess it up. It's not like your mod will be the deal clencher that makes the buyer choose your home. It very well could be the thing that makes the buyer walk away.
Think about it, if you were buying a house from, say, Steve Wozniak (a known good electrical guy, think Apple computer) and he said, 'by the way, I modified the smoke detector so it would...' Would you trust the life and safety of your family with it or would you want it swapped out?
Also, considering all the horror stories there are about the 'buyer from hell' (I know someone personally that had such a buyer, what a major hassle it was and it cost lots in legal fees but that is another story. Their buyer just wanted to back out after the time frame but it still cost the seller legal fees just to clear up the mess.) do you really want that in the mix?
Let's say your buyer gets your notes, is a dream buyer, all is well, and then 3 months later the house burns or something like that. Now you have given them written descriptions of what you did. Who do you think the law/insurance is going to come after? What if they aren't such a dream buyer and they modify your mod and it burns. Now what? Now their insurance company and your insurance company have you on the stand and you say, 'I just added *this* relay, I didn't do *that* to it!". I just don't see the gain here.
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wrote:

I agreed with t he rest of your post, but you really got me with this part. How about if I cut the two wires I soldered to the original smoke detector, and cut off any stubs on the detector itself, and tape the relay wires and roll them up and stuff them away. That puts everything back the way I found it, eletrically at least. Do you think that will leave me safe?
Then what if I leave a note about what I did, so the new owner can put it back the way I made it. Or is that looking for trouble?

It's idealism, believe it or not, and I guess some vanity.. I've improved on the original, and I'd like to see the improvement last.
The warning on the smoke detector is to keep the smoke detector people from being sued, in the case of those who don't know how to do a proper modification. But I started doing stuff like this 50 years ago when I was 8, and after model trains, wall switches, radio, tv, house wiring, more tv and a little bit of other various things, by now I know how to do something simple like this..
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Obviously, it's your choice. I live in CA and when houses change hands there is a specific item on one of the forms regarding smoke detectors in the house. They have to be there. I don't know if this is federal or not. If we were talking electronic door strikes or extra doorbells or something like that, I can understand messing with it. But on something that is specifically called out on one of the forms of the transaction. Obviously some people think it is important.
I've seen other posts that call out, houses built after a certain date and houses built before a certain date regarding if they have to have interconnected smokes or not. Or doing additions to an older house and having to upgrade the smoke detectors from individual to interconnected in order to meet current law. I am not familiar with those laws at all but if they do exist, obviously it is pretty important to some people.
Regarding cutting the wires and putting it back. I work for a company that makes products that customers buy. We get customer returns. It is obvious when people mess with them. How much do you think we should stand behind products that have obviously been worked on by a customer? And our products have nothing at all to do with life safety. I've got to believe that FirstAlert or Firex or whoever else, have legions of really good lawyers that have crossed this bridge before. How much idealism can stand up to that? how much vanity can stand up to that? You said, 'That puts everything back the way I found it, electrically at least. Do you think that will leave me safe?" I am sure you are a great solderer, but I am also sure that there is a pretty good chance that the original manufacturer can detect modifications. How much is a new replacement smoke detector? $10, $60 max? Just change it out with a good one installed. Leave the modified one in a box with instructions on the kitchen counter if you just have to but let the buyer re-install it themselves, not you. Another way to look at it, let's say there is no fire. The buyer doesn't clearly understand the change you did and, during the transaction, says, 'hey, that's great, thanks!'. Then, a month later they read what you did, don't want it, and someone tells them this is a big deal so they overreact and they have a lawyer write you a letter asking you to put a good one in or else. What are you going to do? why hassle with it. Just buy a new one and sell the house with the new good one installed and your modified one in a box on the counter with instructions.
Another poster on this thread mentioned not messing with the originally installed interconnected smokes at all but just dinking around on a separate set of interconnected smokes. I think that is a great idea. the best idea. Have your sandbox to play in, but have the one that counts in perfect condition, unaffected by the sandbox. Build your own sandbox exactly how you want to, play to your heart's content. install, experiment, test, debug, have fun. But leave the original one intact.
You mention you are 58 and have been doing this for 50 years. Surely you can afford two or three or a dozen smokes from Home Depot to play with. Obviously you are smart enough to design your own interconnected system out of those smokes. So do it that way and be safe.
Hopefully I didn't step on any toes. Have a good holday!
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What about those detectors with the built-in emergency light? I presume that's just a flashlight type bulb (not an LED light) and if it can drive a bulb it could drive a small reed relay. Wiring a relay in place of the bulb is a pretty minimal alteration.
Rather than fooling with the noisemaker in each detector you could buy such things (Sonalert or whatever) and place them next to each detector or wherever you feel like so that there is good audio coverage around the house (best place for a detector isn't necessarily the best place for the alarm horns). Run Class 2 3 wire cable around the house. One wire is the feed from some central power source...a battery...a DC supply or a doorbell tranformer (depending on the needs of your alarm horns)...feeding the relays in each detector. 2nd wire is what the other side of each relay is connected to and is also what the horns are connecte to. 3rd wire is common return.
Now when any detector goes off the alarm horns everywhere go off though they won't be the ones inside the other detectors. You could wire them up so they are the horns that sound but I figure it's best to leave them be so that if your whole system fails for some reason (short circuit) at least the one detector nearest the smoke will still sound even if the others don't.
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On Thu, 15 Dec 2005 23:38:19 GMT, Steve Kraus

No comment on your post, but it reminds me of another thing I did that was rather interesting. Couldn't hear the doorbell upstairs when the computer and radio are running, and couldn't figure out an easy way to run a wire from the existing doorbell**
So I took the 3 dollar wireless door buzzer that my mother used before she died (cement walls in her apartment building.) and I took the button half, and soldered a jumper across the button switch on the circuit board.
Then I connected the 9 volt connector of the button par sort of to the doorbell transformer, that is, in parallel with the current doorbell, with a diode in the circuit to give DC from the 18?** volt AC transformer. And screwed the thing to a ceiling joist in the basement.
Now when someone rings the front doorbell, it also powers the button half, the LED lights, and it causes the buzzer in the hallway upstairs to sound.
** (I'm done running wires through the stack. I should have put in some spares but dudn't.)
***The transformer is 18 volts because 12 wasn't enough when I got the seocnd doorbell for the basement. But I think rectified 12 volts, which would have been about 6 volts, might have been enough to power the 9 volt button half of the wireless doorbell. If not, a full wave or bridge rectifier could have been used to get closer to 9 volts.
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wow you're getting some interesting replies. some thoughts from buffalo ny: you may play with extra smoke detectors only in addition to the dedicated approved systems and devices in your home, not interconnect them to the minimum required devices in your building. not permitted to connect other items to the inspected dedicated red electrical smoke detector box circuit or its devices. not permitted: altering a lifesaving safety device. you are creating a hazard for yourself and others. especially if you die from smoke inhalation, where only the stupidity will live on.
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wrote:

Darn, my last ditch plan to solve the problem autonut pointed out was to live here until I died. Then the new owner probably couldn't sue me.
But now you point out that wouldn't be right either.
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