You probably got the older HS1SA (Standalone) model which does not work well with HA although it has a Zigbee module build in.
Check the date code on the little leaflet inside the battery compartment and/or the Zigbee Model within Z2M. It should at least read “SmokeSensor-EF-3.0” (as for the HS1SA-E (Zigbee 3.0)).
If the model reads something like “SMOK_V1x” it wont work as expected within HA (unsupported).
More about the different models HERE.
Thanks for the suggestion. All other devices (around 30 of them from different vendors) work very reliably, so I don’t think it’s the network.
Thank you for the explanation. You’re right, I have the “broken” first generation Zigbee smoke detector from Heiman. I’m still disappointed that they sold an essentially faulty product back then.
I’m hoping to replace them with Thread/Matter enabled smoke detectors in a year or two. But I’m not buying first generation products this time around 
.
what kind of issues there? maybe I can help.
It was great to see this news as just a few days prior I had specced Heiman smoke alarms for a renovation of our apartment building, choosing them over Cavius. The one thing I was personally disappointed by with this decision (since it affected me and my Home Assistant setup but not any other owners) was that Cavius does offer a way to integrate some of their alarms with a home automation setup, while Heiman doesn’t appear to. Specifically the HM2SA-1 model.
We have to use this model here in New Zealand as recent building code changes require multiple smoke alarms per dwelling (hallways, each bedroom, and each level), each with a 10-year battery and they must be wirelessly interconnected so they all sound if one is triggered.
The HM2SA-1 model meets all these requirements and does have a remote (which I put in for each apartment) but there doesn’t seem to be a gateway that can connect each set of interlinked alarms to a Home Assistant (or equivalent home automation) setup.
Does anyone know if such a gateway exists, though? Perhaps I just missed it? Or maybe one is planned for the future?
@CJB I think that you juat bought the wrong model (i.e. you bought a SKU with no wireless capability). The “HS1SA” model with no additional letters in its SKU model number is not a “smart home” connected device. Sounds like the HM3RC series you linked to only support interconnecting smoke detectors using basic single directional RF433/RF868/RF915 and no more regardless.
Heiman sell several different models of smoke detectors that look the same on the outaide, both for various smart home wireless protocols as well as dumb variants with no wireless capabilities. You should therefore also notice the difference in price between those devices if sold by the same seller.
Anyway, to be able to use one with Home Assistant today you should have bought either the Heiman Matter Smoke Alarm (SKU/model HS1SA-M) or the Heiman Zigbee Smoke Alarm (SKU/model HS1SA-Z), of which I understand only the first is currently certified for the WWHA program.
There is also a Heiman WiFi Smoke Alarm (SKU/model HS1SA-W) that can work indirectly via a Tuya gateway but that is not recommended (particularly because it needs an external gateway and partially because batteries do not last long in Wi-Fi devices).