The manufacturer's don't want you to mix an match, as they say they can't "guarantee" the units will operate correctly or to their maximum operating efficiency, but if you install all their units you can!

Shouldn't be a big deal unless manufacturer's have completely different connection guidelines, or wattages, voltages, etc.

Def. verify before.

Well, I'm TRYING to verify before. That's why I asked. :)

The other method I have to verify is to simply clip my meter on to the interconnect wire and press the test button. Frankly if the signal voltages are the same I'm going to wire them up and see if they work. I'm just not at the project house for the weekend (taking a much-needed break) and won't be able to do this until Monday.

Hook it up. When it starts going off or the smokes blow up then you can tell him I told to buy six new matching units. I sure there is probably some code either electrical or fire that requires them to be interconnected and the same.

You're asking for trouble in my experience. I have found that sometimes different models from the SAME manuf. That are supposed to work together have troubles. I wouldn't even bother interconnecting them if they aren't the same brand.Tell your buddy why though.

The funny thing is that the prblems never seem to show up until you have been gone from that job for a month or so!

"is the 'interconnect' standard?"

No, and that is the problem.

There is no standard.

well, tell the dummies who made the dangerous tr recs REQUIRED to make a STANDARD.