Heiman co detector

I have a Heiman co detector set up on Zigbee2mqtt. I know it won’t report actual co levels, but it should report true or false if co is detected.

The co sensor reports ‘unknown’ when looking at Home Assistant devices. the battery reports 100%

I would expect it to say ‘false’ rather than unknown?

If it did say ‘false’, given that the value is read-only, how could I test it (apart from putting it in the car exhaust)?