Getting all 2-Wire smokes to sound

I am hooking up some "System Sensor" model 2WTA-B combination photoelectric/thermal smoike detectors with built in sounders.

These are 2-wire units and are connected in series on zone 16 on an Elk M1 with an EOL at the last unit.

When testing, will one unit activate all the sounders (or is that not possible) or is that the puropose of using a reversing relay? If it is, does it go on the last unit before the EOL or is the EOL even necessary?

I have an Elk -45 siren set up in the attic that can be used if one sensor can not activate the other sounders.
The reversing relay is what is supposed to be used to trip all the sounders. I never got it to work and then just decided it would be better to have a handful of the inexpensive piezo screamers and sound them. You can pick up 2 or 3 of them for the same price as the relay and are much loader and more effective imho.
I need to make these detectors work. It is one of the write ups from the city on the final inspeciton on my new house. I can't get my occupancy certificate without all the sounders working.

Anybody have a wiring diagram for using a reversing relay on 2 wire smokes in series for an ELK m1?
Well, I did not get it working with THIS relay, but you can look at the instructions from it and it should work as in Figure 3. I believe Mike tried also and had issues. After trying a bunch of things I honestly just gave up and did not pursue it further.
I had it working when I had a 2W-MOD2 installed as well. I later took that out when I thought it might be introducing false alarms (it was bad wiring in the last leg).

I then also heard the 2W-MOD2 was not required as the elk understood the cleanme signal (well the system sensor variant). I believe if I hook it back up it will work with the reversing relay, but then it is hooked to the elk as a 4 wire smoke (in effect).

I never got the direct 2-wire approach to work.

I was going to go back and try the 2WMOD2 though since it seemed to work (and would perform some diagnostics as well) and I already have it.

If you need to make it work quickly you might want to try this (the 2W-MOD2 was about $50 if I remember correctly at AO). I think I posted the wiring diagram here for what I got from System Sensor regarding this (it has been awhile).