Carbon monoxide is commonly known as the “silent killer” — a gas that can spread through your home without any color, odor or even taste to alert you to danger. Breathing in carbon monoxide can restrict the amount of oxygen carried throughout your blood and cause breathing difficulties. This is why you should take the threat of carbon monoxide in your home seriously and why a reliable carbon monoxide detector is critical for ensuring your family’s safety.

In its early stages, carbon monoxide poisoning can lead to headaches, nausea, dizziness and general weakness and, if not treated, can be fatal. It’s easy to confuse it with flu, too, making it important to have a carbon monoxide detector in your home. You don’t want to risk CO poisoning with an old or defective monitor. Whether you’re a new homeowner or it’s time to replace your existing detector, we found the best, most reliable models to help ease your mind and protect your home.

To help you get the best carbon monoxide detector, we put a number of popular models to the test, evaluating their ability to detect carbon monoxide at two hazardous concentration levels: 250 and 400 parts per million. Here are three of CNET’s best options for keeping you safe.

Best carbon monoxide detector overall: First Alert CO615

At an average retail price right around $35, the CO615 from First Alert is the perfect carbon monoxide detector if you’re looking for handy features and decent performance at an affordable price.

Highlights include a digital display that shows real-time carbon monoxide concentration in ppm and battery level, a test/silence button for weekly testing and a peak carbon monoxide level button to show the highest carbon monoxide concentration detected. This is a plug-in model that is backed up by two AA batteries (Energizer E91 only). Just pick any outlet that’s not controlled by a switch or dimmer, and that is at least 5 feet away from any fuel-burning appliance. Plug it in and you’re ready to go. The unit can be hung in the wall with two screws and its cord extends at least 6 feet, giving you a little flexibility as far as where exactly you can install it in your home.

This unit ranked third in our quickness of response test. On average, it took a little more than 12 minutes to detect the presence of carbon monoxide at 250 ppm and just over 8 minutes to detect carbon monoxide at 400 ppm. The real-time carbon monoxide reading is pretty accurate, taking only two and a half minutes to catch up to the reading shown in our control device. The carbon monoxide reading on the detector went a little above what our control was showing. The discrepancy between the two readings remained below 7%.

Best carbon monoxide detector on a budget: First Alert CO400

If all you need is a carbon monoxide detector that can reliably watch your back without leaving a hole in your pocket, then the First Alert CO400 is perfect for the task.

Basic features include a single test/silence button and a very loud alarm. It doesn’t come with a digital display or any smart features, but it makes up for what it lacks in fancy looks with performance and affordability.

Typically available for $25 or less, the CO400 was the least expensive carbon monoxide detector we tested, and it was also the fastest at detecting carbon monoxide at both concentration levels. At 250 ppm, its alarm was set off after an average of 10 minutes, 46 seconds and at 400 ppm, it took only 7 minutes, 3 seconds. Those are excellent results, regardless of price.

With its low asking price, the CO400 would also be a particularly good pick for multistoried homes, where you should aim to have at least one detector on every floor. Plus, as a battery-powered model, it won’t add to your energy bill and is immune if you have a power outage.

Best smoke and carbon monoxide combo detector: First Alert Onelink 1042136

Some carbon monoxide detectors can find both carbon monoxide molecules and smoke particles. These are called “combo” or “two in one” units, doubling as smoke detectors. The First Alert Onelink 1042136 stood out in this category. This device got second place in our quickness of response test, detecting carbon monoxide at 250 ppm after only 11 minutes, 42 seconds and, similarly, carbon monoxide at 400 ppm after 8 minutes, 10 seconds.

Despite not having a digital display, the voice alarm will speak to you in English and clearly state the current carbon monoxide concentration. Depending on where you installed your device, it can also tell you the exact location of the emergency. For example, during testing, you could hear the device saying: “Evacuate, evacuate. There’s carbon monoxide in the living room, 265 ppm.” To my surprise, the control device reading for this round was 260 ppm. That amounts to an accuracy error of less than 2%, which is significantly better than anything else we tested.

Additionally, Onelink is a compelling option for those seeking smart functionality. It’s compatible with Google, Apple HomeKit and Alexa. All you have to do is download the Onelink Home app and create a free account. Then, follow the instructions to set up a new device. From the app, you can test or silence your carbon monoxide alarm, interconnect other carbon monoxide detectors in your home and get emergency notifications to your smartphone.

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