The display is on, everything is always 0 (ppm). I've checked every day for sale (about one month) and never seen anything else than a 0th
A LED flashes every few minutes and shows that it is working properly.
I bought the machine after I've read in the news again 2 months ago by carbon monoxide deaths. As owner of a gas-floor heating I feel safer in any case.
Buying is therefore duty over the function I can only guess. But expect due to strict licensing procedures that everything is ok.
