Diode with Smoke Alarm Signal Cable

Thread Starter

Jukebox

Joined Jul 21, 2020
4
Hello,

This is my first post, my apologies in advance if it is not properly formatted for this forum.

I am replacing the smoke alarms in my house with interconnected units. To be up to local code, they must be hardwired, cable interconnected and must all go off in a unit (this place is a duplex).

This duplex has a shared stairwell, that has its own smoke alarm. The building inspector has told me that this alarm must go off if either unit's alarms go off. To this point, I have just had all alarms connected for simplicity. Last night at around 1:30am, the other units alarms went off, triggering our own to sound. As a solution, I am thinking of wiring in two diodes from each unit to connect to the stairwell unit, without sending the signal to the other unit (see attached drawing). The concern that I have is if there is a fire in the stairwell, the alarm will sound, but will not be able to send out an alarm with the cable to both units, which would be required.

Any thoughts on possible solutions? Any help greatly appreciated.
 

Attachments

Thread Starter

Jukebox

Joined Jul 21, 2020
4
Hi Crutschow,

We are not altering the system from code requirements. There is fire seperation between units. The code requires that the common area alarm must sound if either unit's alarms sound.

I'm more focussed on the application of the diodes, or a similar application to achieve the rather unique smoke alarm setup. I've already gone through the code and legal requirements, and this isn't the website for that.

Thanks.
 

crutschow

Joined Mar 14, 2008
34,285
You would need to know the nature of the signal sent between to two, to know how to isolate the signals.

If the stairwell alarm has to activate both your alarms, as well as either of your alarms having to activate the stairwell alarm, then a simple diode isolation will likely not work.
It would require additional logic circuitry.
If the connection between the smoke detectors is a single bi-directional signal, then the direction of the signal current may need to be detected to determine who is generating the alarm, and then generate the proper logic signal to activate the other alarm(s).
 

Thread Starter

Jukebox

Joined Jul 21, 2020
4
The signal cables are a simple 9V on/off signal to tell the other alarms when another is sounding. I agree that the diode solution wouldn't work for the stairwell alarm going out to the others. I was thinking of doing something with a small arduino and some AND/OR options. The problem that I see with that is there is only one signal cable for each alarm, and it's not something that I want to try to add to.
 

djsfantasi

Joined Apr 11, 2010
9,156
I rehabbed an old house into two apartments. I lived in one. One night, I had an out of control fire in a fireplace. My tenants were alerted. Which is exactly what I wanted. When there are two or more units in a single building, it is critical that EVERYONE be alerted when the alarms are triggered.

If you were able to defeat this feature, you are incurring a huge liability. Possibly death.

IMHO, you don’t want to do this.
 

Tonyr1084

Joined Sep 24, 2015
7,853
it is critical that EVERYONE be alerted
100% agree!

Still, if my neighbor's condo is going up in smoke and the stairwell fills with smoke - I'll get an alarm. Late at that, but still an alarm. And there must be more than one way off an upper floor. Fire escapes or a second stairwell.

Best solution is to teach your neighbor how to cancel a false alarm. Something like yelling "I'M JUST COOKING!".
 

Thread Starter

Jukebox

Joined Jul 21, 2020
4
Hi All,

Thank you again for the responses. I would like to reiterate the fact that I am not breaking code with the ask. Additionally, I have 1-hour fire separation between units, multiple points of egress for both units, and you are able to hear when the alarms are going off in the other unit. The point here is that I don't want my dogs freaking out when the upstairs neighbor has decided to cook a smoky dinner. To play devil's advocate, imagine that you are living in a 25-floor apartment building. I don't think anyone here would agree that every alarm in the building should go off when one person has had a minor mishap in their kitchen resulting in a little smoke or steam. I would like to reiterate again that this is not a fire safety website and I am an adult capable of making educated decisions that adhere to local fire code. I came here for circuit help in accomplishing my objective, not a lesson in everyone's hypothetical opinions on how much they love hearing alarms go off in the night.

The two alarm method is a great concept Tonyr, I agree that with this methodology, no diodes or gates are required. Thank you for pointing it out.
 

Tonyr1084

Joined Sep 24, 2015
7,853
The biggest reason why (and I'll speak solely for myself) we sound warnings is because if someone does something according to what we said - or we failed to point out a danger - I'd feel responsible. Suppose you and your family die in a fire because of something I said or neglected to say. I don't want that on my conscience.

You are undoubtedly an adult capable of making your own decisions. And life will mandate that you live by those decisions. If you made a good decision then life will reward you. Make a bad decision and - - - . What price are you willing to pay? And at who's expense? It's not just your life and security, it's others as well. Your decision can have a negative effect on others.
 

crutschow

Joined Mar 14, 2008
34,285
I also like the two alarm idea.
It requires no circuit addition to the existing wiring, which could be a liability issue if something in that circuit failed.
 

Tonyr1084

Joined Sep 24, 2015
7,853
The one remaining thing that concerns me - even with the [censured by self] is that at 2:00 AM when I'm in my deepest sleep and far away from the stairwell and my neighbor's dwelling is burning; I don't think I'll hear the stairwell alarm. Again, it isn't until the stairwell is filling with smoke that my alarms would ring out. Knowing a safe route out depends on choosing the right direction. The wrong direction could lead to a backdraft flashover fire from the stairwell into my apartment and singe my beautiful little eyebrows. These days it's close to all the hair I have left on my head (save for say the whiskers that keep coming back on my chin).

I get it. 25 floors and everyone's alarm is ringing. I've been there. Eighth floor, 10 units per floor; and someone threw out cigarette ashes that were still lit. The basement is where the smoke and fire was detected but everyone got out safe. I think when that darn alarm rang out I swallowed my lips. I only have a line of a smile these days. Also, the building had fire suppression sprinklers that went off as well. Maybe that's what tripped the fire alarm signal.
 
Last edited:

djsfantasi

Joined Apr 11, 2010
9,156
To play devil's advocate, imagine that you are living in a 25-floor apartment building. I don't think anyone here would agree that every alarm in the building should go off when one person has had a minor mishap in their kitchen resulting in a little smoke or steam. I would like to reiterate again that this is not a fire safety website and I am an adult capable of making educated decisions that adhere to local fire code. I came here for circuit help in accomplishing my objective, not a lesson in everyone's hypothetical opinions on how much they love hearing alarms go off in the night.
I respect your decision. My opinion is that it based on a cognitive failure, but that’s me.

I agree that it’s not a fire safety web site, but there is a wide range of experience and expertise represented here. I’m not an electrical inspector nor a fire inspector. But what I am is a landlord. And with that experience comes some fire safety knowledge.

And as I’ve intimated before, what you’re proposing is NOT up to code. And if anything were to happen, as a landlord, if your actions cause me to incur liability, I’m cutting my losses and coming after your ass.

Just because you can’t control your pets.

Im done. Good luck.
 

MisterBill2

Joined Jan 23, 2018
18,176
I rehabbed an old house into two apartments. I lived in one. One night, I had an out of control fire in a fireplace. My tenants were alerted. Which is exactly what I wanted. When there are two or more units in a single building, it is critical that EVERYONE be alerted when the alarms are triggered.

If you were able to defeat this feature, you are incurring a huge liability. Possibly death.

IMHO, you don’t want to do this.
I was going to add that in a duplex any fire is a problem for both parts of the building. Fires do not pay attention to lease agreements.
Of course, if it was only cooking smoke that set the alarms off there are other problems.
 
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