Hard Wired Smoke Detectors for DSC Alarm System

Hope this is the right place to get help on this. I have a 20 year old alarm system with 2 hard wired (4-wire type) smoke detectors attached to a DSC Power 832 alarm system that is monitored by a local service.

I want to replace the smoke detectors and need some advice. I currently have an ESL (Sentrol) 449C and a “System Sensor” 2100 on the system. I’m not sure why they used 2 different brands. While searching for replacements online, I came up with an Interlogix/ESL 541B, and a system sensor 4W-B. (I also found one from DSC (FSA-410B).

There are 2 issues I’d like advice on:

  1. My system sensor 2100 is definitely a 4-wire model but the system sensor website recommends the 2-wire 2W-B as a replacement for the 2100. I know it’s wired with 4 wires (2 power and 2 for the sensor) and it’s wired in parallel to the ESL449C. Do you agree I’d need the 4W-B?

  2. When my alarm system was installed in 2000, it seems there was no requirement to monitor the power line on the smoke detectors (I assume this because there’s currently no monitor circuit on the power line of the smoke detectors). It seems I could add one OR, I may be able to switch to a 2-wire design. According to the Power DSC 832 manual, I could configure the system to use the 2-wire detectors. I have the installation manual (and installer code) so I can make the mod. My question is, should I stick with the 4-wire detectors and add the power monitor circuit or switch to 2-wire detectors.

    One last question: Since I’m buying new detectors, should I get some that are both smoke and heat detectors?


2-wire detectors are certainly easier to hook up and are generally more suited to newer installations, but 4-wire detectors are usually more geared towards retrofit installations like what you have.

If you decide to use the 4W-B, what you would need is an end-of-line relay (not a resistor) that has its coil hooked in-line with the power circuit, and the NC contact wired with the zone circuit. When a detector is pulled or the power circuit goes offline, the relay breaks the zone circuit, causing a trouble. That is how the power circuit is monitored.

While you could completely replace your system with 2-wire detectors, the two-wire i3 series (including the 2W-B) have a compatibility issue where they will only work with certain panels. The four-wire models (i.e. the 4W-B) do not have this issue.

Thanks so much for the thorough reply.

I think our original installer bypassed the line/power monitoring system. He installed the EOL resistor directly on the panel (across Z8 and common). This defeats the purpose of having the monitor at all. I’ll have to fix that.

The reason I’m doing this now, is the alarm sounded at 5:30AM on Monday. The alarm wasn’t set so it wasn’t a break in and there was no smoke or fire and no call came in from our monitoring service. The system only registered a trouble alert. When I called the alarm monitoring service they also said it was a trouble alert. As far as I know, a Trouble Alert won’t trigger the siren (Bell?). That makes me think the detectors should probably be replaced but there’s no evidence in the system that a real alarm was ever triggered (except for the blaring siren at 5:30AM). Either way, they are 20 years old and don’t have the proper power monitoring in place.

So based on your reply should I assume you prefer System Sensor to Interlogix/ESL?

Also, do you agree that I should replace my old ones with models that have both smoke and heat sensors?

I’m only familiar with System Sensor’s offerings. I know that ESL/Interlogix has a line of smoke detectors, but I believe that they only offer wireless models now. System Sensor’s i3 line is reliable, and the 4-wire models work pretty well on older systems.

For just smoke detection, you want the 4W-B. For smoke/heat, you will want the 4WT-B.

Thanks. I ordered two 4WT-B detectors and an EOLR1 for the power monitor circuit.

I just now realized I was misleading and didn’t give you the whole answer.

You were right in ordering the EOLR-1 relay, but you will still also need an end-of-line resistor, which your panel will call for. You will need both to fully supervise both your zone and power circuits, and should be wired according to the following diagram:


Thanks. Yes my panel requires a 5600 ohm resistor on the end of line relay power monitor circuit. I think the original installer bypassed the power monitor circuit by putting a 5600 ohm resistor across the Z8 and common terminals at the panel. No matter what would have happened to the power at the detectors, the system would never register any trouble because it’s always reading the 5600 ohms on the line (that’s cheating - defeats the safety purpose of monitor the circuit).

It’s all good now. The new 4WT-Bs and the EOLR-1 came today and I installed them with the proper power monitor circuit in place at the end of the line. I like how the 4WT-B mounting plate is designed where without the detectors twisted into place, the power circuit is broken and the power monitor initiates a trouble alert. Seems smart.