A carbon monoxide alarm is designed to beep when it detects elevated carbon monoxide levels. Carbon monoxide detectors approved by the Underwriters Laboratory sound an alarm when levels reach 70ppm and remain elevated for between 60 and 240 minutes. The alarm goes off sooner if carbon monoxide levels are higher.
A beeping carbon monoxide alarm should not be ignored. It is important to turn off all fuel-burning appliances, open windows for ventilation and call emergency services if anyone is showing symptoms of carbon monoxide poisoning. Most carbon monoxide detectors have a reset button for silencing the alarm. However, if carbon monoxide levels are still high, the alarm may go off again after six minutes.