I carry a co detector with me at all times. I do not advertise or report on co testing unless, the detector shows a reading (not very common but it happens) In the event that I show a reading, I report the findings. It has helped detect major problems and is a good way to get peoples attention to take action.
I use the UEi CO71A and it has been serving me well for 5 years. Annual calibration is a good practice.