
Kidde Smoke & Carbon Monoxide Detector
120V AC, All Kidde brand hard wired smoke alarms are interconnectable with the KN-COSM-IBA
If you want an alarm that can detect both smoke and CO, the Kidde KN-COSM-IBA Hardwired Combination Smoke and Carbon Monoxide Alarm is our top pick. It's easy to set up and use, and it has all the bells and whistles you might want in a smoke detector. Besides detecting both smoke and CO, it has two voice alert modes: "Fire!", "Warning! Carbon Monoxide!", and "Low Battery!". We tested it in our home, and it detected smoke from a fire about 10 feet away from the unit. It also detected CO from a nearby cooking fire. The alarm is loud enough to wake you up, but it's not so loud that you'll accidentally silence it. It has a test-hush feature, which silences the unit for 9 minutes, and tamper-resistant technology to deter removal of the unit from the wall or ceiling, and it's easy to install. It's also easy to replace batteries. In our testing, the detector was battery-operated, but it's hardwired, so it can work independently of batteries. It has a 120VAC power source with 2-AA battery backup, and it's designed to interconnect with other KN-COSM-IBA models, so you can add them throughout your house.

Kidde Smoke & Carbon Monoxide Detector
Test-Hush Feature - silences the unit for approximately 8 minutes; tamper-resistant technology deters removal of the unit from the wall or ceiling
The Kidde Smoke and Carbon Monoxide Detector is easy to install, and the hardwiring kit provides even more flexibility. It has 9V battery backup, and its photoelectric sensor can detect visible smoke particles. But its carbon monoxide detector is only rated for 10 parts per million, which may not be enough for some rooms. The detector's LED indicators and voice alarm are useful, but it's a shame that it doesn't provide warning for other types of smoke, such as from cooking. The Kidde Smoke and CO Detector doesn't have wireless capability, which our top pick does. The detector is affordable, but if you're looking for more features, our top pick offers more for a similar price.

Kidde 21007624 AC Photoelectric Smoke Carbon and Monoxide Detector Alarm
Front-loading battery with unique battery door design
The Kidde KN-COPE-IC smoke alarm is easy to install, and it's compatible with both hard and battery backup systems. The alarm's photoelectric smoke sensor is more sensitive than ionization sensors, so it detects slow smoldering fires sooner than an ionization smoke detector. The Kidde KN-COPE-IC has a loud 120-decibel alarm that alerts both you and your pets, making it a good choice for homes with pets. The KN-COPE-IC's included 9V battery provides backup power for up to 30 minutes, so you won't have to worry about a power outage during a power outage. The KN-COPE-IC's alarm memory feature also makes it easy to test the alarm without setting off false alarms, and the unit has voice announcements that alert you to when it's silent or quiet, which can help prevent false activations when your noisy pets are running around. The KN-COPE-IC's battery backup feature and voice announcements make it a great choice for homes with pets, but the alarm's loud alarm might be a little loud for households with small children.

Kidde Smoke Detector
Test-Hush Feature - silences the unit for approximately 7 minutes
The Kidde Smoke Alarm with Battery Backup and Interconnect is a reliable, low-cost option that works well in a typical home. It's easy to install (simply screw the detector into the ceiling), and it's painless to replace batteries. It's also equipped with a photoelectric sensor, which reacts more quickly and reliably to smoldering fire particles than ionization sensors, and it's especially sensitive to smoky fires. The alarm is loud enough to wake you up if you're sleeping, and it's equipped with LED lights, which give you a quick visual alert when the alarm has been triggered. The alarm is also equipped with remote control capabilities, so you can silence the alarm with a remote or keypad, and it's designed to use less power than other alarms. However, this alarm has a couple of drawbacks. First, it doesn't have a test button, so you can't test its sensitivity or test its battery without removing it from the wall. Second, while the alarm is easy to install, it can be tricky to connect the unit to your existing security system, and there's no way to connect the alarm to your existing security system without removing the battery.

Kidde Smoke Detector
Test-Hush Feature - silences the unit for approximately 7 minutes
The Kidde Hardwired Smoke Detector with Battery Backup is our top pick for hardwired smoke detectors. It has excellent sensitivity, and because it uses ionization sensing technology, it doesn't miss any fires that regular photoelectric smoke detectors might. The alarm is loud enough to be heard clearly in a bedroom even at night, and the built-in silence button in the base lets you test your detector without having to silence it. The Kidde Hardwired Smoke Detector is easy to install, and its battery backup feature means that smoke alarms will continue to work during a power failure. The detector's bright, easy-to-read display makes it easy to see the status of your detector. It comes with a 9V battery, and when the backup battery runs low, it alerts you. The detector has a removable base for easy installation. The Kidde Hardwired Smoke Detector with Battery Backup isn't the best alarm we tested, but it's an excellent choice for many homeowners.

Kidde Smoke & Carbon Monoxide Detector
Test-Hush Feature - silences the unit for approximately 8 minutes; tamper-resistant technology deters removal of the unit from the wall or ceiling
The Kidde Smoke & Carbon Monoxide Detector is our best and most reliable detector for homes, studios, and apartments with a central HVAC system. With 100 percent optical smoke detection, the Kidde detector's photoelectric sensor technology allows it to detect even small smoke particles, and it offers much-improved detection over our previous pick, the Honeywell 5500. The Kidde detector also has much louder and clearer alarm output than both our previous pick and the Nest Protect, as well as voice alerts, LEDs, and a battery backup. The detector confirms that the detector has detected smoke with a bright LED light. The detector's LED also indicates the battery status. The Kidde detector's battery backup makes it more reliable in the event of a power failure, and it alerts users even if they've forgotten to plug in the battery. The Kidde detector also has two sensitivity levels, but we found that the best setting for a typical home was the medium setting. The Kidde detector has an alarm output that you can connect to other smoke detectors in your building, but it requires special wiring, so we recommend using other Kidde detectors, if possible. The Kidde detector has a dial made from rugged plastic that adjusts the sensitivity of the detector.

Kidde P4010ACS-W Hardwire Smoke Detector with 10-Year Backup Battery Voice Alert and Intelligent Wire-Free Interconnect
Wireless interconnect compatible only with other P4010 Wire-Free models
The Kidde P4010ACS-W smoke detector was more difficult to install than some other smoke detectors we tested, but ultimately it was one of the easiest to use. It has a small, unobtrusive design, and the same beep and voice alert that you'll find on Kidde's other smoke alarms. The P4010ACS-W has wireless interconnects, so you don't need to worry about running wires throughout your home; just plug it into the power outlet nearest where the smoke detector will be, connect the interconnect, and you're done. Installation is fairly straightforward, but if you're inexperienced, we advise you to read the user's manual before getting started. The P4010ACS-W's alarm is quite loud, and while the smoke detector's LED status ring flashes red, it's only visible from a few feet away. The alarm will sound again when the smoke detector detects smoke, and it will also sound again when the battery is low. The 10-year battery life is adequate, but it's slightly shorter than what you'll get with some other smoke detectors we tested.

Kidde 21010407-A i12010S Worry-Free Smoke Alarm with Lithium Sealed Battery Backup 120 Volt AC
Lithium Battery Backup 120 Volt

Kidde 1279-9999/RF-SM-AC Hardwire Smoke with Alarm Battery Backup
Product is highly durable and very easy to use
The Kidde 1279-9999/RF-SM-AC hardwire smoke alarm is among the better smoke alarms we tested. It was easy to install, and was very easy to set up and program, thanks to an online interface that allows users to configure the unit with their names and e-mail addresses. The unit also has two buttons, labeled Test and Silence, that make it easy to test and silence the system without unplugging it from the wall. The alarm has a loud, 115-decibel siren and emits two long, loud chirps when a fire is detected. It also has a built-in carbon monoxide alarm. The alarm has a 10-year sealed battery, which is long enough to make replacing it unnecessary. We loaded a 9 volt battery into the unit, and the alarm worked as expected. The alarm can also be hardwired to a home's electrical system. The alarm's two-way voice communication feature makes it easy to communicate with other units, and the alarm's digital readout makes it easy to see the battery's charge level.

Kidde Carbon Monoxide Detector
Test-silence button - allows for test & silence of alarm
The Kidde CO100A is one of the most reliable carbon monoxide detectors we've tested, and it can detect CO levels as low as 0.1 parts per million (ppm). Its alarm is loud and colorful, and its digital display is easy to read. The CO100A has a 10-year battery life, but it comes with a backup battery that can power it for up to 30 days in the event of a power outage. The CO100A also has an audible alarm that beeps when carbon monoxide levels reach 5 ppm. The display lights up green when CO levels are below 5 ppm. When CO levels are between 5 and 50 ppm, the display shows 5, and when CO levels are above 50 ppm, it displays 50. The CO100A has a bright enough display that you can read it from across the room, but we found that it was harder to see the display in the middle of the night. The CO100A has a built-in 10-year lithium battery, so it doesn't have to be replaced after 10 years. The CO100A is easy to install, and it comes with two adjustable mounting brackets so you can mount it on your wall or on the ceiling. The CO100A is not compatible with Kidde's Kidde Alert XP smoke alarm.