First Alert Combination Smoke & Carbon Monoxide Alarm, Interconnect Hardwire Detector with Battery Backup, SMICO100-AC, 1-Pack

I bought this to replace the six First Alert SC9120B alarms my builder installed about eight years ago. These were very easy to install taking less than five minutes each. I did have a few issues with some of my older models though. The builder put so much wire in some of the junction boxes that it pressed down hard on the alarms making a strap wrench, or a belt, necessary to unscrew them. Also, on one of the units, they used a screw that was too large to secure the mounting plate but there was enough room to wiggle the old plate out.A few notes…This is a direct replacement for the SC9120B but it isn’t a one-to-one match physically. You will need to install a new mounting plate. The good news is that the screw holes on the new model are universal, so they should fit most junction boxes and is very easy to install.The power connector is the same, but the receptacle on the new alarm is smaller. It does help to prevent bent pins, but you need insert the connector straight for it connect securely. When removing it from the SC9120B, I found a pair of pliers useful to get a good grip.Although the units are hardwired, they do come with battery backup using a preinstalled 9V battery. This battery is an ordinary Duracell 9V model and will likely fail in about five years. For hard to reach alarm locations, you may want to get a ten-year battery and replace them. Again, these are battery backups for hardwired alarms, so they really shouldn’t be needed very much, unlike battery-powered alarms.Like the prior model, this alarm has a green LED that indicates it’s plugged in and functioning normally. That LED is about 25% to 50% brighter than the one on the SC9120B and will light up the area around the alarm at night. Most of the light seems to leak out the “Ring” at the top of the alarm right above the indentation. It is possible to put something in that “Ring” to block the light, such as electrical tape, or, if you’re the adventurous type, open up the alarm and use a black marker to dull the LED or snip the LED entirely. Given that the LED serves as an indicator telling me it’s working as intended, and in my case, I’m planning on selling my home during the expected lifespan of the alarm, I’m opting for electrical tape.

work great and easy to installed.

Was compatible with a prior model (wiring) which kept beeping after 9 years and 2 new batteries.Had to take out the old faceplate and replace it - which was the "hardest" thing to do in the install process. Plugged in with the backup battery and worked like a charm.

Easy to install and plugs into my existing First Alert wiring. Hopefully these last longer than the builder grade one's I've been replacing.The base plate that these alarms twists into wasn't compatible with my existing units, which was wishful thinking since it's the same brand, but it was easy enough to loosen the screws, remove the prior and spin these on.Two of the three sets I ordered didn't come with the yellow protective bonnets pre-installed, which isn't a big deal but would have been a nice touch to know they've been protected from dust or other environmental contaminants prior to install.

These detectors and very easy to install. I install the base first using a couple of screws and then I can just put on the detectors by hand. The alarm sound is loud enough to be heard. Plus, the cost of lower compared to the other brands.

I had all of the fire/ CO detectors replaced in my house. They are working just fine.

I bought this as a replacement when the current alarm died. It was easy to install...a little ify having Kitty Grandma on a ladder, but I managed. When testing the alarm the cat went flying, so I guess it's loud enough

My home isn't that old, but the builder-installed smoke/CO detectors started failing. I am not talking about the lame single beeps (always in the middle of the night) that announce that it is time to change the backup battery. No, indeed...the old units made the triple-beep that said they needed replacing. Of course, they chose the middle of the night to fail and no less than three of them failed at once.This package of three is perfect for my needs. These are a direct, snap-in replacement for the originals -- I did not have to change around the plugs or the mount. It was plug in, mount to the ring, and twist to lock. Probably the easiest home DIY project I have had in a while.Pay the extra few dollars, get the direct replacements, save yourself the headaches.