Yeah, my beep tormented me, but no microphones were rented in journey to the solution.
Just a guess, but....
Don't know you have a crawlspace? Renter. (Not that there's anything wrong with that)
Throw your stuff on top of a previous tenants stuff in the closet? Kind of lazy!
CO2 alarm "hidden" on a beam joist in a crawlspace? Kind of odd. (Wrong location in most situations)
Crawl space that clean? Unbelievable. Not in my world!
Beer cans in the crawl space? I would be disturbed if they weren't there....
The knife however.... Wild card.