Smoke Detectors


Senior Member
I've been reading the posts here and looking at 2-wire and 4-wire smoke detectors (this is for residential use). If I understand everything correctly:

1. Run in series using one zone
2. Cannot determine which one went off if you are using multiple
3. Can tell the panel that it needs cleaning

1. Can run in series or as separate zones
2. Can determine which one went off and apply logic to that effect if using multiple detectors
3. Cannot recieve a cleaning signal

If I've gotten the above right, I tend to lean towards 4-wire so I can have an indication that an alarm went off in a specific room. The big difference seems to be the cleaning indication, is this such a big deal?

I also saw one other person saying they just replaced the detectors every few years, is this recommended and cover this as well (sounds possibly more thorough than required).
I would use the term "daisy-chain" rather than " in series" to describe multiple smoke detectors on the same zone.

The limit of only one zone supporting 2-wire smokes is completely dependant on the control panel you use. Some support 2-wire smokes one several or all zones.

You usually would not put all of your smokes on one zone unless you had a very small house with only 1 or 2 smoke detectors because, as you point out, this makes it impossible to pinpoint the exact location of the alarm. Likewise it is unusual to assign a zone to every detector unless you are trying to rig up a fancy annunciator of some sort.

I have about 30 smoke detectors and about a dozen rate-of-rise heat detectors on 8 different zones. I clean and test them once a year and replace the smokes about every 5 years.

I would also note that for fire audible devices I find motorized fire bells to be a superior choice over siren drivers because they use much less current and are easier to supervise when you have a lot of them.
First, let me say I've been lurking here for a while and about to join the crowd and get an M1 from Martin this week. I hate you guys - you make it easy to spend money! I'm replacing an older AT&T 8300 that has served well for 13 years. Hopefully I'll be able to participate more intelligently once I get going.

Smokes are one of the remaining decisions for me. I currently have 2 4-wire units hooked to the panel that are way due to be replaced. These are in addition to the 3 'standalone' detectors wired into the house. My plan is to leave the standalones as they are and replace the 2 others. My dilemma is do I just replace the 4 wires so I can have separate zones (how important is that really if I only have 2 or maybe 3), or do I just go with 2 wires and the GE with the Clean Me? On the surface, Clean Me sounds like a great feature, but is it really that special if you just test regularly?

So, I guess 2 things:

1. How does the GE 521 compare to the System Sensor i3 - is 1 really better than the other at detection?

2. And this is really for Mike... I wonder if by using this module you can have your cake and eat it? Use the GE 2 wire with Clean Me and hook it to any zone on the M1?

Maybe I'm just crazy??? but this intrusion/fire/ha stuff is new to me. Anyway, glad to be here around some very talented people.
I think part of the decision process on how many zones you are going to have depends on your wiring. For instance, no need to crowd everything into 4 zones when you have 16 on the base system alone - you might as well use them.

When I took out my existing system at home, it was only using 4 zones but all of the wires were in the closet but tied together. I unbundled them and now am using a full 16 zones. Might as well, right?? Maybe some items are a little too granular but I really don't mind.
Just to add more fuel to the fire, no pun intended, the smoke detectors will turn on a LED on the smoke detector when they go into alarm. That way you can tell which one of the many that may be on a zone caused the fire alarm. When you are satisfied with finding the trouble maker, you go to a smoke reset menu on the M1 keypad and power is broken to the smokes for 5 seconds to allow the LED indicators to reset. This works for resetting 2 wire and 4 wire smokes.

The verified fire zone is a nice feature to make sure there is a real fire, not a false alarm. When the smoke detector goes into alarm, power is broken to the detectors for 10 seconds. The fire zone is ignored for 20 seconds. If a detector is in alarm or goes into alarm within the next 30 seconds the alarm is activated. Local keypads start beeping immediately when the routine starts.

Thanks for the 2-wire to 4-wire conversion link, it looks interesting. For the small number of smokes you have you might just want to stick with 4-wire units and leave the decision about same zone/separate zones for later. (Assuming they are wired as home runs so you can split them if you want). The main reason for separate zones would be if you want your HA controller to announce which detector is in alarm or trouble.

I have used and liked System Sensor smokes and have also had good luck with Napco FireWolf sensors.
Don't know why something seemingly so trivial in the grand scheme is soooo confusing to me ;) . I read last night on some alarm company site that they recommend 2 wire 100% of the time. They said only reason to put the 4 wire is if you absolutely needed separate zones and the main plus to go with 2 wire is that BOTH power and input lines were supervised. In my pea brain I take that to mean if anything happened like power interruption or cut wires to detector, the panel would notice? Not sure how this would apply to 4 wire. I looked at my old panel last night and it appears my 2 detectors are home runned to the panel and the leads are tied together and wired to same terminal(s). After thinking about it, the 2 scenerios were 1 where I was home and they alarmed. Would I really care which one tripped (am I even going to bother taking a look) or am I just getting out of dodge first and 2 where I'm not home and it tripped. In that scenario even if I called in to reset/check it, etc. would it really be that important to me to know which one it was? My answer to myself was I just hoped the house was still here and I didn't care which one it was.

Sooo, I was all set to go with the 2 wire, when it was like, duh - the 2 wires need to be run in series, but I saw that my wires were home runned - which makes the answer easy if I don't want to run new lines - buuutttt - I thought I read somewhere that you can still wire homerun wires in series using 4 wires? Is that possible or am I 100% having to go with the 4 wires now that I know they are home runned? Of course I should change them anyway because I see the el cheapo installers just used regular wire, not fire rated - but that's another story.

It is true that 4-wire smoke detectors must have power supervision to be legal (and safe). The correct way to wire 4-wire detectors is to install an end-of-line relay at the last detector in the zone (this is also where the end-of-line resistor goes). The end-of-line relay is connected to the smoke detector power wires so that it is always energized. The end-of-line resistor is wired through the relay contacts so that if detector power fails the contacts will open and the resistor is disconnected. This will generate a "fire trouble" at the panel so you know there is a problem.

2-wire detectors just use the end-of-line resistor so are automatically supervised.

An important point to remember about ANY smoke detector installation is that it must be supervised from panel to end-of-line resistor. That means it if you branch off to a detector you must have seperate conductors for the feed and return wires. You can't, for example just run a 4 conductor cable to a 4-wire smoke unless it is the last sensor on the zone. You have to run 4 conductors to the detector and a separate 4 conductors away from it to the next detector in line. If any device is removed it MUST be wired such that it breaks the path to the end-of-line resistor and puts the panel in trouble.

For 2-wire detectors you can use 4 conductor cable in home runs to each detector by using 2 conductors as feed and 2 as return. At your junction you would connect the return pair from the first detector to the feed pair of the second detector etc. The return pair of the last detector is connected to the end-of-line resistor.

With 4-wire detector home runs you have to use 8 conductor cables (or two 4 conductor cables) so that you have separate feeds and returns for both zone and power. You cannot just run a single pair of wires to feed unsupervised power to the detector! The power return from the last detector must have the end-of-line relay on it and the zone return has the end-of line-resistor (connected through the relay contacts).

Remember that your bells or sirens must also be supervised with an end-of-line resistor and must be wired with separate feed and return conductors as well.
Thanks upstatemike. Sounds like my existing install is not right, but who cares as long as I get it right with the M1. Sounds like unless I want to start putting relays, my plan is to use 2 wire smokes with my 4 wire homeruns. I just want to be clear on the wiring. I drew this up - does it look right?


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One question on this that I still dont understand: Why is it that 2 wire smoke detectors can send a cleaning signal and 4 wires can't (logically 4 wires would typically mean more capabilities/information).

I'm inclined to run more cat5e (although need to check on the firewire aspect, suppose the equivalent would be plenum?) and use 4 wire smoke detectors one per zone.

I would run 2 wires but it seems I can't break them out by zone on the elk.
Cat-5 should technically work for home running 4-wire smokes but it might not be legal unless it has a red jacket. Using plenum cable won't help you meet this requirement and is not needed unless you are really running it through an air plenum or duct.

I am currently using a dedicated fire alarm panel that supports several zones of 2-wire smokes and has a separate output for each zone in addition to the common panel alarm. This is a brute force way to interface an Elk panel with several zones of 2-wire smokes but certainly not the preferred approach.
upstatemike said:
The correct way to wire 4-wire detectors is to install an end-of-line relay at the last detector in the zone (this is also where the end-of-line resistor goes).
Ok, so if I were change my mind (worse than the wife - I know) and forget the CleanMe which I wouldn't have anyway if I go with the i3 detector, I may as well use my 4 wire home runs into different zones - I'm prob going to be into an expander anyway.

This EOL relay - is it a special part? From rad shack, ELK? Do you have a link or part number to an appropriate one?