Universal Security InstrumentsM Series Plug-In Carbon Monoxide and Natural Gas Alarm with 9 -Volt Battery Backup, Model MCND401B,Classic White

As a new home owner I wanted to make sure that I covered all my bases for protecting my home. If you have ANY gas appliances this unit is a must!The instructions are very simple and easy to follow. At first I installed the unit in my laundry room to make sure that my new gas dryer wasn't leaking and was happy to find that it never went off. However, the instructions do inform you that you should install the unit in an open area not near any gas appliances as then the pilot will light off a small amount of gas may set the alarm.Overall I am very pleased and highly recommend this to any homeowner.

So... this RUDELY awoke my wife and I at 2am because it detected natural gas. We didn't smell anything and both of our noses work well, but we asked the gas company to send out a person anyway. While we waited, I unplugged the unit and took out the 9v battery because it was painfully loud. After a few minutes I put the battery back in and plugged it in. About 15 minutes later it started beeping so I again removed all electricity from it.The gas company person soon arrived and determined there was a slow leak and began turning off gas lines while measuring line pressure to determine which one was the problem. While he was doing that I found a very slight gas smell behind the stove and the stove turned out to be the problem.Conclusion:This was plugged into a wall outlet on the second story of a 2700 sq.ft. house and detected a slow natural gas leak from behind a stove on the first floor that was only able to be detected by a healthy nose close to the source.The central air was off at the time so there wasn't air circulation/mixing.After the line to the stove was shut off and I finally got the pilot light ignited on the water heater I powered the unit and it no longer beeped.

I purchased this detector a year ago, for use in a second home. It *seemed* to work fine thru last winter when the house was closed up- I say, "seems to have" since it happily sat there with a glowing green light-- never once giving any alarm. Now reading aall the other reviews I was probably living in a fool's paradise since it seems this detector doesn't detect ANYTHING. We reopen the house this spring, put new batteries in all the house detectors, this one included- and 2 days later, in the dead of the night (dead is a good term to use here), this one goes off. There is nothing like a CO/Gas detector going off in the middle of the night to scare the begeezes out of one's self. However there are 2 other CO monitors about the house (it was the CO part of the alarm that went off) and they did not respond. There was no smell of gas, and the window in the room where this detector was installed was open. The beep-code it gave was for CO, not gas, not battery failure, unit failure, or a 'time to replace unit' sequence. The unit was reset by pressing the reset button, and a CO reading of 49 displayed. This was reset to 0, and the unit reinstalled. We all fell back into an uneasy sleep, but with all the windows open. About dawn it went off again, and again displayed the CO level of 49.Being a scientist at heart, I had to conduct an experiment--, so the unit was plug in to an outside, the reading was reset. It did not go off after that but the "49 PPM CO" reading returned. It is plain from the other reviews and my own experience that the unit can not be trusted. It can not be trusted so much so, that it now resided somewhere in our county landfill.

My mother had this exact model installed on her second floor of her house, and a different brand on the main level. A few weeks ago one of her gas burners, the knob was accidentally turned and natural gas was filling the house and we didn't know it until this alarm started going off UPSTAIRS...but the other brand on the same level picked up nothing. So I bought her this extra one for her main level of the house since it sensed the dangerous level of natural gas in her home, but the other brands did not.

Edited June 6, 2015My original review, which I am greatly revising, reads as follows:"This carbon monoxide and combustible gas detector/alarm works very well, is easy to deploy, and inconspicuous. I feel much safer having it in the room when using my ventless gas heater." This was based on the fact that it lighted up and responded to pressing the test button as specified in the instruction leaflet.As time went on, I began to realize that I occasionally got whiffs of the natural gas typical skunky smell (from an odorant added to make leaks detectable). The detector never indicated the presence of gas, so I assumed I had a hypersensitive nose. However, I recently began to wonder if the detector was actually able to detect natural gas, so decided to test the detector with a known natural gas leak. I removed the head from one of the burners on my gas stove, put the fully powered and operative detector atop the open hole where gas comes out, and briefly turned on the burner, without the igniter operating. The smell of gas was strong, and I actually started to feel a little dizzy. I waited several minutes to see if the detector would respond. It never did - it proved to be totally insensitive to natural gas. I tried this test 3 times, absolutely no response to natural gas. This may be a defective sample, it is hard to believe Universal Security would still be selling these if they don't work. However, I will not be buying any more of their products after this experience.

WENT DOWN MY BSMT. WHEN I HEARD THE ALARM BEEPING CONSTANTLY. DIDN'T REALLY SMELL ANYTHING BUT CALLED GAS CO. ANYWAY. GUY CAME & HIS METER DIDN'T DETECT ANYTHING. I OPENED THE BSMT. DOOR & ALARM STOPPED AFTER A FEW MINUTES. CLOSED BSMT. DOOR & ALARM STARTED AGAIN AFTER A FEW MINUTES. THEN GAS CO. GUY STARTED TO LOOK AGAIN. HE NOTICED THAT THE GAS METER DIAL WAS MOVING EVEN THOUGH NO GAS APPLIANCE WERE BEING USE. THE UNIVERSAL ALARM FOUND THE LEAK BEFORE HE DID.