In a different thread, there were comments about getting old detectors. I can vouch this was not the case here – the three I bought were manufactured in December 2018.
(YMMV depending on which Amz fulfillment center it gets shipped from, however.)
It’s about a guy who thought his landlord was leaving weird notes in his house while he was at work. But he was actually writing the notes himself and forgetting due to carbon monoxide poisoning.
Notice that this doesn’t have a replaceable battery. Apparently you just throw it out and get a new one.
Says in description that 9v battery is recurred.
I bought one a few weeks ago and it came with a 9v battery