This Carbon Monoxide Sensor warns of the presence of CO in the cockpit—the spot will turn gray/black when CO is in the air. The spot on the detector returns to normal color after it is exposed to fresh air. You can use this passive sensor is your personal and portable CO sensing device. With the adhesive back, stick it on the panel or dash for a semi-permanent installation, or wear it on an ID badge or on a lanyard. Unopened sensors have a shelf life of 3 years, indicated by the expiration date on the package. Once removed from the packaging, the CO sensor will last for 12 months. Made to be used in conjunction with an electronic alarm.