CO detectors must meet the requirements of the most recent Underwriters Laboratories standard 2034 or the requirements of the IAS 6-96 standard. Avoid using cardboard or plastic detectors that change color and do not sound an alarm. They require you to look at the device to determine if CO is present. CO concentrations can build up quickly while occupants are asleep, and these devices would not sound an alarm to wake them. Although they look solid, garage walls are no barrier to combustion byproducts.
Carbon monoxide seeps in from the garage into the house through the shared walls and ceilings.
Exhaust gases can seep into the house when a vehicle leaves or enters the garage or you start a snow blower or lawn mower, contaminating the air with carbon monoxide and air laden with dirt. Deaths have occurred in homes next to enclosed garages in which drivers have let their vehicle motors run. Car exhaust produces combustion byproducts resulting in ultra-fine coating of oily, sooty, black residue in your home. If you notice soot in your home, or your carpets are dirty - this could be the result of your car exhaust. Do not run a vehicle, snow blower, or lawn mower inside a garage.