2-Wire VS. 4-Wire Smoke Detectors - Which Is Best For Your Alarm System?

Hey guys. Hayden here again from Alarm System Store. And today I'm just going to be doing a brief explanation of the difference between two-wire and four-wire smoke detectors. So I like my visual representations. So I basically just have a main board for an alarm system here. And I have a few smoke bases that we're going to be using, along with these short wires to simulate our wire runs or whatever the case might be.

So. As I mentioned, the main topic is just going to be two-wire and four-wire smokes and the differences between them. So we're just going to start with two-wire smokes because those are the most simplistic. Essentially, every alarm system that offers hardwired compatibility with two-wire smoke detectors is going to have a single input/output that it is going to use to power and supervise two-wire smoke detectors. So, for example, on this DSC NEO here, we have PGM2 here. It's basically a single output terminal that provides power to these smoke detectors as well as supervises the wiring chain. Now with two-wire smoke detectors, the main thing to keep in mind is that two-wire smokes have to be chained off of that one input on the panel. So no matter what your situation is, no matter what build type you're doing, whatever the building layout is, you're going to be chaining your smoke detectors off of that one input. And the system is just going to have a single smoke zone. So some systems actually provide an actual zone identifier for that. However, systems like the DSC NEO and the IQ Pro and things like that, they basically just have a smoke zone that is active at all times, and you only really see it if there is a trouble or the smokes go off. It doesn't give you name identifiers for each of your smokes or give you really any identification whatsoever, other than the fact that the smoke alarm has been triggered. 

So if we were going to set up a two-wire chain of smokes, we'll just use two of these real quick. All you would do is essentially take a couple of wires, and you're going to chain your smokes as I mentioned. So you're going to go directly from the panel to the first smoke. And then from the first smoke to the second smoke like so. And essentially you'll just do that all the way until you have covered all of the spots throughout your building that you need smoke detectors in. So that makes for a very easy installation, because all you have to do is just run basically a single wire run all the way through to the end. Each spot that you're going to have a smoke, do a little twist in it so you have some extra wire to play with. And then when you go back to actually install these, cut the wire, attach it, go down to the next one, and do the same. On your very last detector, you're going to put your end-of-line resistor, and that's all you have to do. So it does make installation running wire that whole bit a lot simpler, especially when you're in a situation where you can freely run wire throughout a building.

However, in a situation where, you know, we have multiple floors, let's say we have these two smokes on a single floor in our building. However, we also have a second floor and we want smokes up here as well. You can do that by just again continuing the chain all the way up until you get to that last smoke. So on and so forth. However, once that goes off, let's say this detector on the second floor goes off. The only thing we know is that a smoke detector in the building has gone off. Now, in most cases, as long as you have central station, you're going to have the fire department on the way already, etc., etc.. However, knowing where those smoke detectors are can provide a potential prevention of the fire spreading. And that is where four-wire smokes come in. 

So four-wire smokes can be zoned out. And what that means is every single one of our smokes can be on an individual home run to the alarm system, and we can provide each one a name, so long as we connect each one to an individual zone on the alarm system. So if we wanted to do that, let's say we had the same setup where we had four detectors in the building. So this is what it would look like. You home-run every single wire to the panel on the system. However, all of these smokes are going to be powered by the same output. So, for example, on this DSC NEO, again we are going to use PGM2 for the power. So that is going to provide our resettable power for our smoke detectors. However, since we have the power and the zones split into two different sets of wires, basically you would have your red and black going to your power, and then the green and yellow for each of your smoke runs is going to go to an individual zone. Now in the alarm system, we can go in and plug in a name for each one of those smoke detectors. So with all of our smokes labeled, we essentially have identifiers for each one of those. So let's say our northwest bedroom goes off. We can see that on the keypad. Or we can see it in our Alarm.com notification or whatever the case might be. Central station is still on their way, if you have that service. And so long as you can do so safely, you can go directly to which smoke triggered because you know which one it is. And if you have a fire extinguisher on hand, you can attempt to put out the fire or at least prevent it from spreading. Make sure that anybody in that immediate area can get out as well. So on and so forth.

So that is one use case of four-wire smokes. Like I said, you can have all of them home run just like we had there. However, you can also create multiple chains with four-wire smokes. So let's say we have a first floor, and we don't need individual names for let's say it's a relatively small building. However, what we can do is we can create chains that cover the first and second floor. So just like this, we would have one chain. Again, all of these are going to be powered by the same output on the system. However, this chain is going to be connected to, say, zone one. And this chain is going to be connected to zone two. So now we know if zone one goes off, it is our first-floor detectors. If zone two goes off, it is our second-floor detectors. So there is another use case of four-wire smokes. That is why anytime you have a multi-floor building, it is recommended that you go with four-wire smoke so that you can separate them out this way.

So although just a moment ago I was explaining how important it is for you to know which smoke was triggered. It is also important for central station monitoring as well, because when the monitoring center contacts and dispatches the fire department, they can, as long as you have your zone identifiers set up properly, they can tell the fire department exactly where the fire started so they know how to respond. Not only better, but quicker, more accurately, and so on and so forth, once they arrive on scene. 

Now, one thing to remember when it comes to four-wire smokes is four wire smokes cannot supervise their own power output. So because both our power and our zone are on separate circuits now, the system can only supervise the zone circuit. So we can only see if the detectors have been triggered. However, if your power goes out, for, you know, a like a chain of smokes, it doesn't know that. So there are modules that are called end-of-line relays that you would attach on your last smoke in each chain that basically monitor the power wires. And if you lose power to that circuit, it will essentially cause a trouble condition on that zone to let you know that there is an issue with that chain of smokes. So if you do all individual, you know, four-wire smokes all connected to their own zone, it is recommended that you use an end-of-line relay with each one so that if any of your smokes lose power, you'll know about it.

So key takeaways for the differences between 2 and 4-wire smokes. Two-wire are going to be run in a single chain off of the alarm system. No matter how many detectors you end up having. So it is best used for either smaller builds where you're not going to be using a lot of smoke detectors, or single-story buildings where basically no matter which one goes off, it's going to be kind of in the same area. With four-wire smokes, they can be run individually to individual zones, or they can be run in multiple sensor chains like we have here and have their own unique identifiers for each chain. So they work better when it comes to multi-story buildings or somewhere that you are going to have a lot of smoke detectors in a larger building. And it's important to know, you know, which one has gone off, so that you can try to prevent the fire from taking out everything.

With two-wire smokes, both power and the zone are supervised by the alarm system. So no matter what happens- whether you lose power, the sensors trip the wires, or whatever the case- you will know about it right away. You don't have to worry about, you know, attaching any extra modules. For four-wire smokes, the system can supervise the zone side of these sensors; however, it cannot supervise the power. So you have to add those end-of-line relay modules so that you can ensure that you don't lose power on any of your chains or individual detectors, or whatever the case might be.

Now real quick, just to cover the alarm system side of things. Any system that supports two and four-wire smokes is going to support these configurations of two and four-wire smokes that I've gone over. However, the way they attach to the alarm system may be different. For example, like I said, this DSC NEO for two-wire smokes PGM2 both powers and supervises the detectors. For four-wire, PGM2 powers them, and then you have your zone inputs for the supervision of the circuits. Systems like the Honeywell Vista, however, do it a bit differently. Instead of having an output like this for all smoke detectors. Zone one is used for two-wire smokes, so Zone One on the Honeywell Vista both powers and supervises two-wire smoke detectors. It does offer on-board outputs that you can use for four-wire; however, they're kind of weak in terms of how many smokes you can run. I think it's only like 2 or 3, depending on what models you're using. So for Honeywell Vista, if you would like to zone out your smoke detectors, it is important that you pay attention to the power draw of all your smokes and if you need an extra like relay module to power them, that you add that to your system so that you can make sure that all your smokes have power and so on and so forth. So all systems do it slightly differently. However, as far as the detectors go, they all follow the same premise. Two-wire smokes are chained off the panel; four-wire smokes can be zoned out.

So that's pretty much it for this video. If you guys have any questions, by all means leave them down below. Hopefully that was informative enough, and you guys learned something. If you did, if you don't mind, leave a like and subscribe, and I will catch you guys on the next one.