A First Alert carbon monoxide (CO) emergency sounds like four loud, continuous beeps followed by a brief pause. It operates at an extremely high-pitched volume (around 85 decibels) to ensure you are woken up. Some models will also use a voice prompt to explicitly warn you of an emergency.
To know if your First Alert carbon monoxide (CO) detector is working, look for a flashing green or red light, which indicates it is receiving power. To fully verify it is operational, press and hold the "Test/Silence" button until the alarm sounds.
Carbon monoxide alarms alert you with four beeps. A single chirp means the battery is low or the detector should be replaced.
4 beeps and a pause: This indicates there is carbon monoxide in the air, seek fresh air immediately and call 911. 1 chirp every minute: This indicates the alarms batteries are low and you should replace them. 3 chirps every minute: This indicates the alarm has encountered a malfunction and requires replacement.
Carbon monoxide alarms use different alert sounds than smoke alarms to avoid confusion. They typically emit beeping or chirping sounds, which are lower in pitch compared to the high-pitched tone of smoke alarms.
It is also a good idea to know the signs of a potential CO problem:
You can tell the difference by listening to the sound pattern of the beeps.
Carbon monoxide (CO) false alarms are most frequently caused by expired sensors (usually 5–7 years), low or dead batteries, or dust and debris clogging the sensor chamber. Other common culprits include high humidity, cooking fumes, or the off-gassing of household chemicals and aerosols.
If you are not usually exposed to cigarette smoke, but you have a reading of 4 or more, you may have been exposed to carbon monoxide through faulty heating or cooking appliances. It is important to check that your heating and cooking appliances are safely installed.
A low battery is one of the most common and easily fixable causes of a beeping carbon monoxide detector—but it's not always as simple as it sounds. Even a freshly installed battery can fail if it's not seated properly, the wrong type is used, or the contacts are corroded.
The OSHA personal exposure limit (PEL) for CO is 50 parts per million (ppm). OSHA standards prohibit worker exposure to more than 50 parts of CO gas per million parts of air averaged during an 8-hour time period. The 8-hour PEL for CO in maritime operations is also 50 ppm.
Many false alarms are preventable and stem from simple issues with smoke and CO detectors, including:
First Alert carbon monoxide (CO) alarms—like all UL-listed residential detectors—use a combination of gas concentration and exposure time to trigger the alarm. They will alert at the following thresholds set by UL 2034 standards:
Carbon monoxide (CO) is a silent, odorless, and invisible gas. Because you cannot see or smell it, you must rely on carbon monoxide detectors, warning signs around your appliances, and your own physical symptoms to identify its presence.
Yes. A green light is completely normal and means your carbon monoxide (CO) detector has power and is actively monitoring your home. It is very common for this green light to blink once every 30 to 60 seconds to save battery life.
Two common warning signs of carbon monoxide (CO) poisoning are dizziness and a dull, throbbing headache.
Yes, opening a windows helps by diluting carbon monoxide (CO) with fresh air. However, it is not a substitute for evacuation and professional repairs.
A carbon monoxide (CO) detector beeping 3 times every 30 to 60 seconds typically indicates a unit malfunction or end-of-life warning, rather than an emergency. It means the detector needs to be replaced immediately, as it is no longer capable of sensing dangerous gas.
Symptoms of Carbon Monoxide Poisoning
Low levels of CO poisoning can be confused with flu symptoms, food poisoning or other illnesses and can have a long-term health risk if left uncorrected.
A carbon monoxide (CO) emergency is indicated by 4 loud, rapid beeps followed by a short pause.
If your carbon monoxide (CO) alarm is going off, always treat it as a real emergency first. Because CO is an invisible, odorless, and potentially deadly gas, never assume an alarm is false until you have safely investigated.
If your carbon monoxide (CO) detector goes off and then stops, it could be a transient gas leak (like a neighbor running a heater or engine), a faulty battery, or an end-of-life warning. However, always treat it as a real emergency first to rule out dangerous levels of odorless gas.
Smoke detectors look very different from carbon monoxide (CO) detectors. Smoke alarms are typically ceiling-mounted discs with visible air vents, while CO detectors are often rectangular, can plug into wall outlets, and frequently feature a digital display showing gas levels.