If your house is all electric and you have no gas burning appliances in your home then you could likely get by without having a carbon monoxide detector installed in your all electric house.
Still if you drive a vehicle or run a lawn mower and park it inside an attached garage that attaches to your house then the car and lawn mower can give off carbon monoxide so I would have at least one carbon monoxide detector in the room next to the garage and maybe one carbon monoxide detector in the garage just to be safe.
Never run your car in the garage if it's an attached garage because it produces carbon monoxide which can get into your house.
Back the car out of the garage and then let it idle outside with the tailpipe being outside the garage.
If you have an all electric house then you might also need an emergency backup heat source that may produce carbon monoxide when used so it would be a good idea to have a carbon monoxide detector installed for that purpose as they're cheap and can save your life.