Yes, this seems to indicate at the very least they sound when the alarm is triggered? I have not heard mine sound yet when testing.
How are you testing? Pressing the test button is not a proper test. I use an actual smoke detector tester spray to test. It will sound the siren every time, assuming the alarm is working properly.
Hmmm, I received a call before I could finish entering the PIN to turn off the alarm (Wife burnt something on the indoor grill). My siren also went off. Come to think of it, I returned my dual smoke/co2 alarm because that one didn't work. I think their was a problem with the communication with the ZWave network even after I rebuilt it. So I went with the smoke detector without the co2, since I really don't need it as my home doesn't have gas at all.
I have not tested mine yet. I was more interested in the fact it appears you can also sound off the First Alert devices when the Iris alarm is triggered.