When I got my first CO monitor, I put it low in the lower level of the house, not too far from the furnace.
When the furnace was replaced 4 years ago, the techs came up and replaced the thermostat and installed a new CO monitor. The tech put it up on the wall at the same level as the thermostat. I questioned the placement and he informed me that I was wrong. Please advise me.
They generally advise to put them closer to the ceiling, but not too close so as to be placed in the area of stale air in the corners. There are directions in the packages when you buy them. I have six of them in my house: garage, two redundant detectors downstairs, two redundant upstairs at one end of the hall and one at the other end of the hall.
Best regards,
DDM