These use 868 MHz RF for the interlink. The RF link is automatically configured when the detectors are added to a z2m (or any other supported coordinator) network. The interlink is otherwise completely independent of zigbee and will work just fine even if the coordinator is down. I assume this fulfils the “not using software” requirement for interlinked detectors.
Not sure if that is an answer to the original question? There is no way to trigger an alarm using zigbee, so they can’t be “interlinked in HA”. The interlinking is fully automatic and independent of both z2m and HA after the initial interview is finished.
The detectors expose a few sensors via zigbee which can be used for automations/monitoring in HA: smoke, tamper, test, temperature, battery. The “smoke” sensor can probably be used to trigger external actions in HA, like calling an alarm number or similar.
Note that the temperature sensor is primarily for detecting fires. Both resolution and update frequency are too low to be useful under normal condtions.
There’s also a 230V version: Schneider Electric W599501 control via MQTT | Zigbee2MQTT
I have no experience with that one. One interesting fact to be aware of tis that it is physically larger than the battery powered detector