What does ppm mean in a carbon monoxide alarm?

[VanTravis]

ppm in a carbon monoxide alarm represents concentration. Carbon monoxide alarms can be categorized by usage into residential carbon monoxide alarms and industrial carbon monoxide alarms. Additionally, based on installation methods, they can be divided into wall-mounted or fixed carbon monoxide alarms and portable carbon monoxide alarms. A carbon monoxide alarm detects the concentration of carbon monoxide gas in the air through a carbon monoxide sensor, converting it into an electrical signal whose magnitude correlates with the concentration of carbon monoxide. Carbon monoxide alarms are classified by the type of sensor used, generally including semiconductor carbon monoxide alarms, electrochemical carbon monoxide alarms, and infrared carbon monoxide detectors.