Elk with 2-wire smokes not alarming

I wired the RRS MOD like the diagram shows for 2 wire smokes, using the SAUX power on the ELK. I used output 3 as the relay to activete the RRS MOD, but any output will work.

Set the RRS MOD switch to the ON position and add the folllowing rules:

To activate the smokes

THEN TURN Smoke detectors (Output 3) ON

To reset the smokes I used a task so that I could reset them remotely on a false alarm:

THEN ACTIVATE Task 01 (Task 1)

THEN TURN Smoke detectors (Output 3) OFF

The first rule is a work around. The rule needs a timer since the "whenever" will only activate on the first transition of the zone to the "Violated" state. This way it resets the logic engine to test zone 16 every five seconds to see if the zone was a false alarm. Also it will not re-trip the alarm once the other rule resets the smokes and the RRS MOD resets. You could probably use a shorter time frame, but hey, polling the fire zone every 5 seconds is probably plenty.


Senior Member
The 10 volts you are seeing when the Bosch detector goes into alarm is not low enough to trigger the M1 2 wire alarm threshold.

It seems that each manufacturer has different pull down resistances in their detectors. The two wire sensing circuit for the M1 was approved with the System Sensor Smoke Detectors.

In order to pass the UL requirements, we had to tighten up the alarm thresholds which made some detectors not work. System Sensor is an industry leading smoke detector so that is the one we chose to model.


Active Member
gcimmino said:
Spanky, could you please comment on compatability of the 2WTA-B? This is the same as the 2WT-B with an internal sounder. I'm presuming this would not be a UL listed (tested) configuration, but would it function? It seems to have the same max current when in alarm as the non-sounder versions listed.
Spanky, sorry for the confusion. I understand that the current M1 won't work with my existing Bosch 2 wires.

My recent question was specifically on variations of the supported System Sensor detectors. I'm resigned that I'll have to replace my Bosch detectors with System Sensor ones for proper operation.

The only question is that my Bosch ones have local sounders and the equivalent function in System Sensor is the 2WTA-B, which is NOT among Elk's list of compatible models, while it is a member of the 2WT family.

So my specific question is: Is there a technical reason why the 2WTA-B will NOT function properly with the M1? I do understand that Elk may not have submitted this combination for UL testing, but I'm wondering if it would function?

Thank you


Senior Member
have recently installed 6 2WTA-B's in series on an ELK using the the RRS-MOD from System Sensor to make all the sounders activate when any one detector activates and it works like a champ.

Sounds like (ok bad pun) they will work. Just check the current in alarm. Since you only have 3 detectors I would assume you would be fine.

The best test is to use a can of smoke to trip the detectors one at a time and then all three at once. Obviously once the first is in alarm the sounders will be going on all three if you have the reversing module.

I prefer 4 wire detectors so I dont have to deal with this issue. I also like one detector per zone. But thats just me.

PM me tomorrow if you want me to look for the System Sensor specs. They publish it somwhere on the net also but its hard to find.