Carbon monoxide detectors have become an increasingly common safety device in homes, schools and businesses. These electronic sensors provide advance warning that carbon monoxide (CO) concentrations have reached dangerous levels indoors. A CO detector must be capable of distinguishing between low-level sources of carbon monoxide such as cigarette smoke that -- while unhealthy -- do not pose an immediate life-threatening risk to the building's occupants.
Cigarettes vary in the amount of carbon monoxide they release: on average, it falls between .03 to 3.5 mg per smoke. Most carbon monoxide detectors do not sound their alarms at such low levels. However, a roomful of people smoking may be enough to set off the device.
Depending upon your type of carbon monoxide detector, cigarette smoke could cause a "low level" reading. This may not be enough to sound the alarm, but the detector would show minute levels of the dangerous gas in the air.
Keep in mind that carbon monoxide detectors are not smoke detectors, unless you buy a dual device that provides both types of detection. A cigarette left burning unattended can start a fire that will not set of a carbon monoxide detector at all.