Amazon.com: Customer Reviews: Kidde 900-0234 Nighthawk Carbon Monoxide Alarm, Long Life AC Powered with Battery Backup and Digital Display
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on June 1, 2009
Kidde makes good CO detectors. We've had several Nighthawks for years and they've worked well (at least we think so, never had a CO problem). Our previous version was the the COPP-3 (we had a couple of experiences with the low battery chirping-- a nuisance in the middle of the night--and once, it happened again shortly after we had put a new battery in. Others have had many more problems in that regard--see reviews).

It was time to replace them. We first bought 3 Kidde KN-COPP-B Front Load Battery-Operated Carbon Monoxide Alarm with Digital Display--but ran into several problems (see my review). The biggest problem was that Amazon's stock was old (the detectors were over 2 years old) and the warranty was only for 5 years. Other downsides are that they required mounting and were only battery operated! We returned them making use of Amazon's consumer-friendly return policy.

We then bought this model. It has these great features.

1) Comes with a 7-year warranty (new feature, old had 5 years).

2) Shows the CO level continuously. It's reassuring to see the red LED showing 0!

3) Has a well designed, clearly organized printed manual (a small booklet).

4) Operates off of AC with a battery backup. (That's helpful as you have the best of both worlds!)

5) Has peak level button (this is a new feature).

6) Battery included.

A Big Downside:

A big downside is that they eliminated the plug on a cord. That was really helpful as it gives the user real flexibility in where to put the detector. In our bedroom, the only accessible plugs are beside a dresser in a corner or between bookshelves and the TV stand, meaning less air flow. With the old model, you could plug in the device and then with the cord, put the detector on the top of a bookshelf or stand. Much more convenient.

The other problem, which plagues all the CO detectors and many other products on the market, is the infuriating, hard plastic packaging. It's hard to open and I even cut myself on it. There are alternatives that are just as secure but much friendlier to the environment and the customer!

We still have a year or two left on one of our old ones, so we're keeping that. We also bought a First Alert CO615, which does have the cord, and we'll probably move that into our bedroom when the time comes. (But it has more negatives--see review!)
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on December 28, 2009
The alarm on this device could wake the dead. It is larger than it appears, and covers both receptacles. Installing the back-up battery isn't fast--you must unscrew a little screw to get the battery door open, and reinstall it to get the door closed again. Believe the instructions when they tell you to plug it in as soon as the battery is installed to avoid the alarm going off. I didn't time how long before the alarm sounded, but it isn't long at all based on my personal experience. I suggest you install the battery in the room where you are going to install the unit. It is reassuring to see the red zero on the displays. I have two of them, and would buy the product again.
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Long-lived CO alarm requires replacement at the 7-year mark, and has an annoying tamper-resistant feature (but it can be turned off).

After learning that home carbon-monoxide sensors have a finite lifespan, I decided to replace my oldest Nighthawk (well past its "expiration" as far as I can tell), with one of this new product line that is supposed to be effective for longer.

I found a few interesting differences between this new model and my older ones. One is that while this model is rated to last 7 years, it actually has planned obsolescence-- at the 7 year mark (from 1st power-up), it begins to chirp every 15 seconds. That means in 7 years, you must replace or discard the unit. Since I doubt the sensor completely fails between 6yrs364days and 7yrs, this seems like an attempt by Kidde to ensure sales volume (or to reduce liability by picking a "safe" cut-off). I'd have been happier with the ability to either service the unit (replace the sensor rather than discard the whole), or just have a "replace unit" warning light. I'd think it better to have a unit working with diminished capability, than to have no unit at all.

There are also alarms tied to the unit receiving AC power, with the unit sounding a loud tamper-warning otherwise. Eg, once the unit has a battery in it and is plugged in, if you were to simply unplug the unit, it would sound a very loud, persistent alarm. So to move it, you have to hold down the test button for 2-seconds first, to get a 2-minute unplugged grace period before the tamper-siren sounds.

I'm not sure if this feature is aimed at consumers with small misbehaved children, or aimed at those paranoid about malicious actions, but it seems out of place in an adults-only household. Reading the manual, I did discover that this feature can be disabled (hold down the button on the back, and use a screwdriver to slide a recessed switch to a disabled position). I'm glad the "feature" can be disabled, but considering the number of reviews here that mention the tamper-alarm, this work-around seems non-obvious.

Like most recent alarm devices, this unit will beep regularly when it has a low battery (a feature not present in my oldest Nighthawk), but thankfully it does have the ability to silence that beeping (for 12 hours) by holding down the test button (since these batteries seem to always fail during the middle of the night).

The manual states that using the recommended brands of 9v batteries, this unit will run on battery-only
for 20 hours.

I haven't had any CO problems, but this unit seems like it'll do the job, but I dock 1-star for overly noisy warnings and planned obsolescence.
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VINE VOICEon November 3, 2009
Set up was easy. Love the digital read-out. And I love that in 7 years the unit will tell me it's time to replace it. Nice sticker on the top to write in the date myself too.

My only complaint, if you want to call it that, is that you have to hit the button in the back to kill the sound that you hear continuously if you unplug the unit from the ac. Glad I figured that out before the first power failure or the unit would have gone on and on.

Overall, a great unit at a great price.
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on February 15, 2012
On 12/09/11 purchased Kidde Carbon Monoxide Alarm Model KN-COP-DP-LS 900-2034. On 2/02/12 Alarm sounded with Error code 999. Called Kidde Customer Service who said 999 is a defective unit code and they sent a new one. After one day of use the replacement went off with the same error code. Went on Amazon and other review sites and they talked of problems with the same unit. When I went back to Lowe's where I made my original purchase the clerk said other people had problems with the same model.

A CO2 alarm is to save lives but when a loud alarm goes off in your bedroom at 2AM for no reason it may cause more that just being startled. This alarm certainly doesn't allow you to sleep well knowing your protected from Carbon Monoxide.
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TOP 500 REVIEWERon October 22, 2014
I originally purchased three First Alert carbon monoxide alarms (First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm with Battery Backup and Digital Display - two in 2008 and one in 2010) here on Amazon.com for placement in different locations around my house.

One of these CO alarms - most likely a 2008 purchase - has just recently given up the ghost and gone into permanent error mode on the display which means that it's time to purchase a new replacement unit since the alarm's rated useful service life of about 7 years has expired, apparently just a bit on the early side (by about 1 year).

Well I just ordered a replacement alarm from Amazon, but it wasn't the identical First Alert model. Instead, I decided to purchase this comparable CO alarm by Kidde (Kidde 900-0234 Nighthawk Carbon Monoxide Alarm, Long Life AC Powered with Battery Backup and Digital Display - see my review) which I prefer for several reasons based upon my more than 6 years of experience with the aforementioned First Alert CO alarm.

1) The Kidde CO alarm is a truly dedicated plug-in unit with battery backup. The entire unit must be plugged directly into an AC outlet of your choosing where it can be rotated from the vertical to the horizontal (or anywhere in between) to provide a more convenient fit as needed.

Since all of the AC outlets that I use for these devices are easily accessible, I have never had any use for the small, snap-on AC adapter with an extra length of cord that the First Alert model provides for easier access to inconveniently located power outlets while keeping the more bulky main alarm housing at a more distant and convenient location.

This specific feature has been nothing short of a nuisance over time with the small, flimsy brackets that hold the AC adapter in place on the back of the unit eventually breaking off resulting in an alarm that no longer can be plugged flush into the wall outlet unless you resort to less-than-perfect repairs to reattach the AC adapter with tape, etc.

Unless you definitely need and/or want to mount your CO alarms at a distance from the power outlet, the Kidde CO alarm is the clearly more durable, all-in-one, easy-as-pie solution that you should purchase.

2) Since the batteries usually need to be changed no more than once each year, backup battery accessibility (2 AAs) is "too convenient" on the First Alert CO alarm. The batteries are located behind a relatively flimsy hinged plastic door/latch directly beneath the main LCD display on the front of the unit. This door opens relatively easily, but closing it can frequently be a problem as one or the other of the hinges seems to catch on something and provide significant resistance when attempting to do so. I have on more than one occasion thought that the door might break, but it never did.

The Kidde alarm provides battery backup via a 9V battery that is kept nicely out-of sight and out-of-mind in its battery compartment that can easily be accessed by removing a single screw with a Philips screwdriver. No worries about any potentially broken plastic doors, hinges or other parts here!

3) The display on the Kidde CO alarm is a very nice, bright, always easily legible (even at night and at a distance) red LED which in my opinion is far superior to the LCD display that First Alert uses on its model. Unless you activate the much needed back lighting by pressing the appropriate button, the LCD display is very difficult to read.

4) The error code malfunction on the display (and associated beeping/chirping) indicating the useful service life of the alarm has expired and it needs to be replaced is not set to occur until 10 years after first powering the unit on with the Kidde alarm. The First Alert alarm is set to do this after only 7 years have elapsed and in my case (see above) this apparently occurred after only 6 years.

5) The manufacturing date of the CO alarm can be easily and clearly read on a sticker located on the back of the Kidde unit while trying to find the specific manufacturing date of the First Alert alarm (I am referring to my units from 2008 and 2010.) is like playing a game of hide and seek. I still have not been able to determine the manufacturing dates of my First Alert alarms.

Note that unless there are small children or other individuals at home who are likely to tamper with the CO alarm by unplugging it, etc. there is really no need to activate the optional anti-tampering functionality (alarm arrives with this feature turned off) on the Kidde CO alarm. Who needs or wants a loud warning alarm to go off every time that there is a power outage of any sort - definitely not me!

Nevertheless, as far as the actual functioning of the CO alarm itself is concerned (accuracy and sensitivity, testing capability, last recorded peak CO value, etc.) both manufacturers do indeed provide the consumer with essentially comparable devices. From a purely technical perspective, you really can't make a wrong decision in choosing either one of these home carbon monoxide alarms.
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on July 11, 2010
Both 2 of these to replace my 7-year-old Kidde CO detectors of a similar model, one per floor. They plug into any wall outet. I like the battery-backup and the digital CO level display. If you press a button, you can see "peak" CO level since the last reset. Am using these peak level readings to try to track down occasional very low levels of CO that are too low to be dangerous or trigger any alarm. I am pleased with these CO detectors. My only complaint is that I wish I could see the instantaneous low level CO readings [but such pro CO detectors normally cost much more].

One important point. There is something you have to do to prevent the unit from beeping every minute on battery backup if the AC power goes out. Follow the instructions to do that and you will like this unit much better as a result.
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on December 3, 2011
I like seeing that zero, indicating no carbon monoxide, at all. I don't want any CO, after the old stove released 400ppm without triggering the previous alarm that was sitting right next to it. That alarm was at the end of the warranty period but tested OK. In fact, our new stove put out 60ppm once and less a few times. Turns out that's legal so long as the level is low and for a short time. So, I check the zero frequently. Replace old alarms; run a venting fan or open a window *anytime* you use your oven. // I recommend you disable the 'tamper-proof' alarm before you plug it in the first time, unless you need to know it's unplugged. Otherwise, it will alarm when you move it or change the batteries. peace, mjh
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on December 23, 2009
After owning the other Kidde CO detector with digital display (Part Number 900-0076 Model KN-COPP-3), I was about to buy another one until I found this Kidde 900-0234 for a much lower total price (as compared to Lowes or Costco) here on Amazon shipped to my door. The old one lasted about 7 years without any problems then gave me an error code and stopped working. Looking into it, these Kidde CO detectors apparently have a shelf life of 7 years and that was true for my case. There is not much difference between the two; this one is a plug in and the other has a cord with a small plug in transformer. Both have the same features and work the same.

One thing people should be careful of is the shelf-life of these, luckily mine had only a 2 month old build date stamp on the back. The 7-year timer is suppose to start the count down after initial plug-in, but Kidde seems concerned about sensitivity as these age, probably for liability reasons. Seems like most people would want the newest one for best sensitivity and longest life.

So far so good after one day of use.
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on July 5, 2013
This product of its kind. No question. Previous old model alerted us in middle of night of dangerous levels of chemical in the air when marine battery in basement that powered b/u sump pump had gone bad, so we know its necessary and they work for intended purpose.
Issue is with the item automatically telling you after a certain number of years that it no longer functions. As in our just previous model. Unfortunately it was two years short of the warranty time. Found out that this current one I just bought was manufactured a year ago which shorts me on one years warranty time. Warranty should start when it is first used, not when first mabufactured and sitting on shelf of manufacturer or seller.
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