Kidde Firex KF20 Optical Smoke Alarm - Mains Operated with Battery Back Up

Used these to replace two aging and about to expire Firex 120-1123E smoke detectors. Same fitting plate, same wiring connector so just pull the battery protection tape out, plug in the existing 3-pin power and attach to plate. All done in less than a minute. Tested and fully functional. Includes a Duracell long-life backup battery.Service life is 11 years (July 2034) which is very good as I’ve previously had issues with what was obviously ‘old stock’ with much shorter service life.These units do not use an Americium 241 radioisotope source as most modern smoke detectors use optical (infra-red) detection. Better for the environment and easier to dispose of.

I did my research so I could use the base plate and electric plug of the old one (a Firex 4973) and avoid the cost of an electrician and still be safe to DIY this job. The KF20 is that kind of simple to install replacement. I only needed ladder, a flathead screwdriver to push the little button in and turn the whole front cover anti-clockwise. Then I just gently (with a little nudge under the clip ) the plug off and voila... ready to receive the new one. The new one had a long yellow strip of plastic over the enclosed battery that needed to be removed when installing to get the battery to operate, but confusingly on the strip in small lettering it stated "permanently connect ac power before removing - which is impossible to do as the battery cover is held down by the plug when it is inserted. So I did a quick call to their technical department and the gentleman said "no go ahead remove it before installing the plug bit. No problem but we only write this on there because sometimes people remove this plastic strip and then wait weeks before installing the whole thing and without it being plugged into the mains the battery drains whilst it is laying around. Ok, once I knew that I pulled the strip, heard the loud beep of contact, sign the battery is working . Then got on the ladder attached the 3 pin plug, folded the wiring neatly and twisted clockwise the cover onto the base, nice little click ... And all done and dusted. I have gone and ordered a new one for upstairs too ( that was a ionised one, but they have been phased out ), but I checked and base plate for that one (he said on the phone) fits as well with this model too and so does the plug. Lets hope that one goes as smooth as this one : less that 10 minutes, including the call. Even a 59 yr old woman can do this installation, lol! Love how this brand keeps it simple and really customer friendly with same base plate and plugs.... some mobile phone companies could learn a thing of 2 from these guys : )

I needed to replace my old Firex 4870 smoke alarms and didn’t want to have to do any mains rewiring or replacing the ceiling mount to fit new ones.The Amazon listing isn’t very helpful in that it doesn’t have a picture of the back of the smoke alarm, so it’s not possible to tell if they will fit or not. I’m attaching with my review a picture of my old smoke alarm (on a dark background) and a picture of the replacement (on an orange background). As you can see they match exactly and the new one fitted perfectly on the old mount and the old wiring connector. If your smoke alarm looks like mine on the back then this will be the replacement for you.

I had two of these. I installed them a couple of years ago. A few nights ago, the one on the upstairs landing decided to set itself, and the linked one downstairs off at 4 in the morning (why do false alarms always happen when you're asleep?) I could not get the thing to reset so I ended up ripping it off the ceiling mount breaking the mount in the process. Since the one downstairs still seemed to be working fine, I ended up buying the same make and model as a replacement. The old mounting box wasn't a Kidde box. The new one is. I did find the new Kidde box more difficult to fit than the old one and the alarm more difficult to fit in the mounting box (there is significantly less room for wires).

Great product as a replacement changed all 4 in less than 10mins, base plates and cables did not need to be changed but they are supplied if you wish to do so

I bought two of these to replace out of date smoke alarms which had capacitor back up not replaceable batteries. Note that the old alarms were attached to a pattress which made fitting these alarms very easy. If you have to screw the base plate directly to the ceiling, you will need to hide the wiring in the ceiling void. In my case, fitting was straight forward and took minutes, took off the old base plate, put on new one, attached the quick fit connector to the alarm and then twisted the alarm onto the new base plate. Both alarms are inter connected.Would buy again.

Good buy

Replaced faulty alarm upstairs which was linked to downstairs one. Easy switch and good instructions