Carbon Monoxide can spread throughout your house or apartment building from something as simple as a blocked or leaking vent from a heating unit. You cannot smell CO and the first signs are feeling ill. If this occurs at night, you may not wake up again. If you don't have a detector, you should buy one (or more) for sure. Place them in the bedrooms or just outside of bedrooms in the hallway. A battery unit is easier to mount in the hallway between two or more bedroom areas, plugs seem to be hard to find in this area.
I'm not seeing a deal for two detectors, but if it's for two, it's a good deal. If it's for one, not so much...
And FYI, check the manufacture date on the back of your CO detectors if you have them. They should be replaced every 5-7 years. Just because the electronics work when you press the test button, that does not mean the CO sensor inside the unit is functioning.
Thank you for this information and possibly saving my life.
I've given you non-life saving reputation points,