In the northeast U.S. Zillow and their related sites (they own a few real estate sales/rentals sites) is where the majority of rental listings show up. Though keep in mind those are also markets with tons of real estate brokers doing the listings & whatnot. Plenty of owner/landlords also use those sites but I’m not too sure if it’s the same in other parts of the U.S.
Those Zillow sites also have room / roommate search listings but a lot of people tend to join local Facebook groups for that or maybe use apps for that.
It’s the same here in New Jersey, or at least the city I’m in. Recently a fire inspector came by the condo building I was living in & failed ~ 60% of the units because they still had the old style replaceable battery smoke detectors. Apparently going forward we are/were supposed to be using sealed battery smoke detectors & replace them entirely every ~10 years when they stop working.
EDIT: Not sure if that’s OP’s problem unless their alarm company is so cheap that they keep giving OP really old detectors to replace with.