not including fire hydrants and the other obvious places
the combustion equation is fuel + O2 CO2 +H2O by using a CO2 fire extenguisher you remove the oxygen (O2) and stop the fire burning Fuel +CO2 - no fire
Check with your local fire department and they will be GLAD to come to your house and show you where to put up all your detectors and also what type of fire extinguishers to have and where to hang them. And it's a good idea in another aspectthe fire department refreshes themselves on your location. They may also provide window stickers for bedrooms and pets.
I think smoke detectors is one on each floor. Carbon monoxide detectors should be near bedrooms and on each floor.
