See All Carbon Monoxide Detectors


Est. $35
June 2013
by ConsumerSearch

Combination carbon monoxide smoke detector

  • Voice warning alarm
  • Loud
  • Runs on three AA batteries
  • No CO level display
  • Sensitive to cooking smoke
  • Rear-access battery compartment
Where to Buy

Bottom Line

Owners love that the Kidde KN-COSM-B, a combination smoke alarm and carbon monoxide detector, talks to them. Its verbal warnings -- "Fire! Fire!" and "Warning! Carbon Monoxide!" -- ensure it won't be turned off and ignored. It has an ionization smoke alarm that generally reacts faster to open flaming fires than the photoelectric type, which is less likely to react to cooking. As a result, a few owners complain their units are overly sensitive to cooking misadventures.


Effective, but sensitive to cooking smoke. This Kidde combination unit is an ionization-smoke sensing alarm, meaning it detects invisible fire particles associated with fast-flaming fires sooner than a photoelectric alarm. Because of this, it's important to follow the directions to keep the device out of the kitchen, several owners warn, otherwise it will go off frequently. One user writes that his alarm sounds with the small amount of smoke generated when his oven is turned on.

Another dissatisfied Amazon user recalls leaving the house, thinking the fire in the fireplace had been extinguished. After returning an hour later, the whole house had filled with smoke but none of the smoke alarms had gone off. That experience convinced him to replace all of his alarms with photoelectric detectors. Users appreciate having the Test/Reset/Hush button. This disables the alarm for 10 minutes in case the alert was simply a response to a burned meal. However, if the smoke level continues to build, the alarm will reactivate.

Ease Of Use

Voice alarm is hard to ignore. Owners laud the all-in-one features of the Kidde KN-COSM-B and love that it emits different spoken warnings, as well as beeps, when it detects a life-threatening situation. The clear verbal warnings effuse an additional layer of urgency that is hard to ignore: "Fire! Fire!" and "Warning! Carbon Monoxide!" The alarm also has a low-battery warning and Hush Mode to silence alerts. The alarm does not display current CO levels but does have a peak CO level memory function. Pressing the test/reset button resets the memory as does taking out the batteries.

This Kidde alarm has a loyal following for its effectiveness. But, many owners stick with the same model in order to reuse their old mounting base. Since the device has a rear-access battery compartment, owners must twist the unit off the base to replace the three AA batteries. However, the alarm twists on and off fairly easily. The unit has a battery safeguard ensuring that it cannot be mounted without the batteries installed. It has a standard 85-decibel horn, but several gripe that it's too loud and advise others to wear earplugs during testing. Installing the batteries incorrectly also incites a super-loud tone, claims an owner. "Your ears will buzz for a while after you set up this alarm."


Sturdy, but inconspicuous. Owners praise the unit's sturdy feel and unassuming look. The manual instructs owners to install the three high-quality alkaline AA batteries, which are included, and change them twice a year. However, owners disagree about how often they need to change them. Some grumble that they have to replace the batteries every one to two months, while others declare they can go a year without doing so.

One user reports that his lithium batteries last a year. After seven years from initial power-up, the device will chirp every 30 seconds, indicating it is time to replace the unit. The Kidde comes with a label for writing down its expected expiration date. One owner, who purchased a defective unit, praises Kidde customer service for promptly sending him a replacement.

Where To Buy
Kidde KN-COSM-BA Battery-Operated Combination Carbon Monoxide and Smoke Alarm with Talking Alarm

Buy new: $64.97 $32.95   68 Used & new from $9.98

In Stock.

Featured StoresStore RatingNotesTotal Price
eBayeBay rated 3.83 (1281 reviews)1,281 store reviewsIn Stock. Buy it new & now! with eBay Buyer Protection$31.75

Our Sources

1. publishes the reviews of the five best products and services in each category, bestowing special honors to one. Two combination alarms, the Kidde KN-COSM-B and the Kidde KN-COSM-XTR-B, were named two of the four runners up. The Kidde KN-COSM-B earns a score of 4.25 out of 5 for its all-in-one features and its hush button.

Review: Kidde KN-COSM-B Combination Carbon Monoxide and Smoke Alarm with Talking Alarm Review, Kerri Ryan, Aug. 22, 2011


Nearly 450 Amazon owners reviewed the Kidde KN-COSM-B, giving it a score of 4.3 out of 5. About 63 percent gave the unit a perfect score. Owners laud the unit's all-in-one features, easy installation and efficiency. Complaints focus on the unit's sensitivity to cooking smoke and a couple instances of defective units.

Review: Kidde KN-COSM-B Battery-Operated Combination Carbon Monoxide and Smoke Alarm with Talking Alarm, Contributors to, As of May 2013


Nearly 40 owners reviewed the combination alarm on Home Depot's website, giving the device an overall score of 4.6 out of 5 stars. A majority praises the unit's few false alerts, talking feature and easy installation.

Review: Kidde Combination Smoke and Carbon Monoxide Alarm Battery Operated with Voice Alert, Contributors to, As of May 2013


About 45 people reviewed this combination alarm on, giving the device a 4.4-star average. About 70 percent of users gave the unit a perfect score. The handful that gave only 1 star complains of receiving malfunctioning units.

Review: Kidde Smoke and (CO) Carbon Monoxide Combo Alarm, Contributors to, As of May 2013

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