First Alert CO605 vs CO615 Review

If you have an attached garage, a gas stove, or a fireplace, you should also have a carbon monoxide detector. This by-product of combustion can cause both illness and death, but it can’t be seen or smelled. And therefore the best place to put a CO detector is near where you sleep.

First Alert sells a variety of carbon monoxide alarms, so it can be a little challenging to choose which one is the best for your home. We’ll review two of them here to help you decide.

First Alert CO605 Carbon Monoxide Plug-In Alarm with Battery Backup, 3 Pack

First Alert CO605
First Alert CO605

The First Alert CO605 comes in a three-pack which is perfect for a larger home. Not only does it plug into any standard electrical wall outlet, it has a battery backup in case the power goes out. And First Alert even sends you the 9-volt battery in the box.

You won’t need an owner’s manual to understand how to use this alarm. It has one LED light that illuminates when it detects unsafe amounts of CO, or carbon monoxide. And it also emits a piercing 85 decibel sound to alert you to the problem.

Right in the center of the front of the detector you’ll see a single button. Its dual function lets you test the alarm and also silence it if needed.

Finally, here are a few tips about caring for your carbon monoxide alarm. First, since CO is about as dense as regular room air, it doesn’t matter if you place the detector near the floor or the ceiling. Second, the electrochemical sensor inside the alarm stops detecting after a number of years. The test button only confirms that the electronic parts are working properly, not the sensor. Be sure to replace your detectors every five to seven years to be safe.

More features of the First Alert CO605 alarm:

  • Comes with two backup 9-volt battery, user manual, mounting bracket, and Alarm Action chart
  • First Alert offers a 7-year warranty


First Alert CO615 Plug-In Carbon Monoxide Alarm with Battery Backup and Backlit Digital Display, 3-Pack

First Alert CO615
First Alert CO615

The First Alert CO615 carbon monoxide alarm also comes in a three-pack, ideal for homes with multiple bedrooms. And it offers a little flexibility with regards to where you can place it. It plugs into a standard electrical socket, plus it comes with a 6-foot long power cord and AC adapter. But it doesn’t matter if you mount it close to the floor or near the ceiling, it can detect CO all the same.

The electrochemical sensor inside is very accurate for measuring carbon monoxide. It also tends to last for quite a while longer than other types of sensors, but many manufacturers recommend replacing the alarm every five to seven years to be safe. The Test/Silence button on the front of the alarm lets you confirm that the electrical parts are working, but it can’t tell if the sensor is functioning properly.

Besides electrical power, the CO615 alarm can operate on two AA batteries. This is essential for detection if the power goes offline. And regardless of the power source, the detector will emit a shrieking 85 decibel alarm to alert you. It also illuminates an LED light on its front side.

The backlit LED display reveals both the battery status as well as any amounts of CO detected. According to safety standards established by Underwriters Laboratories (UL), the CO615 will sound an alarm if the carbon monoxide levels reach 70ppm, then again at 150ppm and 400ppm. Each increasing amount of CO leads to more frequent alarms.

In case you weren’t aware, a healthy adult might not react to a 100ppm concentration of CO for up to four hours. Then that person might develop a headache. But 400ppm can cause a headache in as little as half an hour, and kill an adult within two hours.

More features of the First Alert CO615 alarm:

  • Comes with two AA batteries, AC adapter with 6-foot power cord, and user manual
  • Covered by a 7-year warranty



Either one of these two carbon monoxide alarms is a wise investment. They have sensitive and accurate electrochemical sensors, plus they run off two different power sources in case of an outage. The main advantages to the CO615 are the LED display to view the status and the 6-foot power cord for flexibility in placement.

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