I have a 1915 1-1/2 story bungalow craftsman, which I'm slowly trying to restore.

In any case, I've started adding some hard wired smoke alarms and CO2 detectors thoughout the house as I tackle an area. So far, I have a combination smoke/CO2 alarm in the basement utility room, a smoke only in the living space in the basement. On the main floor I have a smoke/CO2 detector in the hallway that feeds three bedrooms and a bath and I have a smoke only at the top of the stairway for the 2nd floor, which is open at bottom, but door at top. These are all wired!

I plan on installing a wired smoke only in the basement laundry, and either a smoke (possibly a combo) in the study at the top of the stairs and a combo unit in the attic space/future storage closet and possible furnace room on the 2nd floor.

I then have battery only units in pretty much every other room. Should I try to switch those out to hard wired or is it not worth the effort/cost. I guess the question is should the bedrooms be hard wired or not?

The other question is are the CO2 alarms really worth the extra cost? I realize the danger and my mom lost her mother to CO2 poisoning during a house fire, when my mother was younger. I've just had several people tell me the CO2 alarms don't really work.