I have looking for references to my earlier comment where I mentioned that some newer automobiles do not emit much carbon monoxide. I found it in the instructions for my Nighthawk CO detector on page 6-1.http://www.kidde.com/utcfs/ws-384/Assets/900-0076.pdf
Q. I tried to test the alarm (see below) and it still reads “0.”
– by running the car in the garage
– by holding it to the tailpipe of the car
– by putting it next to the furnace vent
A. DO NOT try to test your alarm by doing any of the above!
Testing the alarm using any of the methods listed above usually
does not yield satisfactory results and could in fact be dangerous.
To accurately test the alarm, please follow the guidelines given
on page 1-5,6.
Never operate a vehicle in a closed garage, as high levels of CO
can be built up in a short time. With an attached garage, dangerous
CO levels develop inside the home as well as within the
Attempting to test the sensor function by holding the alarm next
to a tailpipe or furnace vent may not cause a reading on the display
because today’s vehicles emit very little CO once the engine
reaches operating temperature. Likewise, many of today’s high
efficiency furnaces emit very low levels of CO.