I also have 2 of these since yesterday, and was wondering the same… Indeed you would expect some decent documentation (at least on the zwave level) with these kind of products, but alas…
I haven’t yet been able to verify it, but based on what I have read on Z-Wave - Home Assistant I have a theory (aka guess) about what most of it means (when I say testing below I mean I have pushed the test button a few times and made the siren go off via the switch 
):
Devices that support the Binary Sensor command class will create one (or more) entities starting with binary_sensor . For example, if the node is door_sensor then the binary sensor entity will be binary_sensor.door_sensor .
These will normally be on when the sensor is active, otherwise they will be off . Some devices use on for closed, and some use on for open, and some devices allow you to change how they report.
So I guess the binary sensor “Smoke Detector Sensor” is the easy way to tell if the alarm is going off (as it seems to toggle also when using the test button or manually activating the siren - but need some more experimentation to make sure)
Devices (usually sensors) that support the Alarm command class will create entities starting with sensor , and with some generic suffixes, and a suffix that relates to the supported alarm class. For example, the smoke detector lounge will have an entity sensor.lounge_smoke , and possibly also sensor.lounge_alarm_type and sensor.lounge_alarm_level . If the device creates a binary_sensor entity, it is recommended to use that rather then the sensor entity.
This further reinforces the idea that the binary sensor and the alarm level/alarm type have an overlapping purpose. However, neither level nor type have so far changed during my testing, so maybe they only indicate an actual smoke alarm, not a test. type seems to be used for the kind of alarm (see page linked above), eg 2 for smoke, level details the alarm a bit more (again, see the zwave entities page for more)
the sensors that end in smoke and burglar I guess are then the alarm_level sensor for the smoke senor and the tamper detection (when you remove the device from it’s baseplate) respectively. No clue about what the values mean exactly - as 254 is unkwnon event according to the entities page, and one of them has been on 0, 2 and 254 during testing (but I didn’t monitor these during quick testing, so not sure what state they correspond to).
sourcenodeid : Reports the sensor that generated the alarm - this is only valid for Zensor Net based devices
Wild guess: if you link up two or more of them ,so they all go off without a controller when one goes off, it reports which node has the actual alarm?
In the logic above, the system sensor should then also be an alarm level, but it doesn’t seem to correspond to what is listed for that on the entities page, as “1” is hardware failure, but it seems unlikely we all have failed devices Maybe it is an indication for the 10 year battery, and will change when that is nearing it’s end? The battery level reported by the device is the battery in the z-wave module, not tthe detector itself, according to the manual.
Would be interested if anyone can verify or contradict these guesses, or if anyone already tried contacting the manufacturer and asking for more detail?
