M1 and "uncertified" 2-wire smoke detectors

[miamicanes]

I know that Elk officially says that GE 500-series detectors that aren't on its (tiny) list of certified smoke detectors aren't compatible with the M1, and that mixing different models isn't allowed...but is there any real engineering reason (as opposed to regulatory "anything not officially allowed is forbidden" paranoia) to believe that a 2-wire loop of smoke alarms on z16 consisting of 2 521BXT detectors, a 521NCSXT, and possibly a 521B or two, would actively malfunction in a real system?

According to GE's own compatibility chart, the 521B and 521BXT are type "S09A" or "S10A", depending upon whether dip switch 1 is on or off, and the 521NCSXT is always type "S10A".

The only hardware issue I can see is that the 521NCSXT might not trigger its own sounder unless it personally detects smoke, because it depends upon polarity-reversal to sound its internal alarm when another detector reports smoke, and I don't see any obvious way that the M1 could reverse the polarity of zone 16 without borking zone 15 (which shares z16's NEG) in the process. If there's a warning somewhere about not using zone 15 when zone 16 is doing "smoke detector duty" (or at least a caution that it has to be capable of dealing with reversed polarity), I haven't seen it yet.

On the other hand, going by GE's documentation, it looks like I could solve THAT problem by sticking a GE ESL-405-01 or ESL-405-03 module between the Elk and smoke detector loop, and using one of the 12v outputs with a rule that fires when a smoke detector gets triggered.

 

[Del91574]

Compatibility charts are only for listing if a particular smoke/series will work with a panel, not if they work together on the same loop. They also typically list the maximum number that can be installed, even though (curiously) most panel manufacturers will list the maximum numbers as less.

Mixing makes/models of smokes, especially 2 wire units, is a bad idea. In the case of a 2 wire setup, mismatched units might not trigger the loop. The 521B and 521BXT are from the same series, so that's not the issue at hand.

I have personally witnessed different series of smokes not functioning on the same loop as well as different manufacturers smokes doing the same. I've witnessed 2 different manufacturers 4 wire units, which are supposed to be universal, do the same. We've run across it in existing systems where units become obsolete or need to be replaced, as well as with add ons....it's, unfortunately, just the way it is. I, myself, wouldn't chance it as a pro.

For what the smokes really cost, is it worth taking a chance?