Great and super easy to install.

This is a good multi-sensor AC powered smoke alarm with battery backup. Easy installation. So far, so good.

Replaced some 20 years old Firex units. Unfortunately the plugs and mounting brackets need to be changed but it was an easy job.This contractor pack saved money but no adapter cables included. Just bare lead connectors to replace my old ones to wire nuts which is really all you need.Comes with decent Duracell batteries but I tossed in some energizer lithium AAs before I put them up since I have a few high ceilings that are a pain to deal with. If you swap batteries do them one at a time and the battery disconnect pull tab won't fall out on you.The hard part was figuring out which breaker they are powered by. I pulled the battery (maybe not necessary) from an old one near the breaker panel and left it dangling where I could eyeball it. Cycled breakers until I saw the LED go dark. In my case it turned out to be the upstairs bathrooms breaker which didn't bother anyone for the time I needed.Always a good idea to dead check your 110vac at the wire nut before you start swapping out connectors. Also if you plan to use the interconnect orange wires you will want to at least start the strip on those wires before you climb the ladder.Junction boxes are pretty standard so the original screws fit the new mounting bracket no problem. Wear some eye protection for the inevitable bits of paint or texture or drywall that will rain down upon you. Each will chirp once when you pull the battery tab so don't leave your ear too close.

There's good news and bad news about this product. (Detailed review ahead.)This product is highly rated by the leading consumer testing magazine. And it's priced competitively on Amazon.I ordered 6 of these, and all arrived promptly, packed together, but in individual smaller boxes, all well cushioned.Five of the items arrived perfect, and installed easily (but more info on an important installation detail below).One of these detectors arrived with a significant manufacturer's defect. See the attached photo for a clear illustration of the defect, which made this detector uninstallable. The electrical pins inside the device were improperly positioned. This defect also interfered with the opening/closing of the battery door on the new detector. Amazon handled the exchange promptly and courteously.Now, about the installation of the OK units: There's also good news and bad news.Good news: The connecting pigtails included with the new First Alert smoke detectors are identical to the pigtails in my 10-year-old First Alert same-model detectors, which these are replacing. That means it was not necessary to un-wire and re-wire new pigtails into their wall boxes before replacing each detector. I was able simply to disconnect the old pigtail from the old detector and plug it into the new detectors. Easy! And safe!Bad news: First Alert has very SLIGHTLY modified the round plastic mounting base for the new units, compared to their own 10-year-old design. This means I had to remove the old mounting base and replace it with the new one. It's an easy step, no problem. But because the new mounting base has a smaller diameter (a "trimmer" design), the new bases expose a ring of unpainted/unwalpapered wall/ceiling surface, which requires patching. First Alert has ALSO SLIGHTLY modified the turnscrew plastic locking design of the detector, so it no longer secures completely to the 10-year-old design. This, also, means the old mounting bases cannot simply be left in place, with the new detectors simply attaching to them.In a couple of highly-visible and not-easily-patched wallpaper locations, I decided to leave the old mounting bases in place anyway (preserving the wallcovering's appearance), and discovered that the new detectors ARE able to hang fairly securely (but not perfectly) on the old bases. This is an imperfect workaround, but it DOES work, especially since the detectors are in no danger of falling off the wall (they're hardwired, electrically). Using this method will require a bit of care (a two-handed job) when changing batteries annually, to avoid pulling the detectors off their mounts. But it's not difficult.A final note: Regardless of whether these detectors are attached to their OLD mounts or to the NEW ones, the distinction is invisible from below. In fact, the wallcovering issue with the new, trimmer bases is more noticeable than the new detectors attached to the old mounts.

This was easy to install. It's so much easier to attach the detector to the mounting plate than my old smoke detectors! I really like the latch feature that makes it easy to identify which detector triggered an alarm or a low battery chirp. I also like that it uses AA backup batteries, which are much cheaper than the 9V batteries my old detectors used.I used these detectors in most of my house. I also put one on each floor for CO detection. The 3120B is great because it's a dual sensor detector. The two models interconnect successfully so any detector can trigger an alarm from all of the rest. (The compatibility is assured in the 3120B instructions. And I tested it myself, too.) If one of the talking detectors is the one that detects a problem, a voice will announce if it's smoke or CO. If one of the non-talking alarms detects a problem, there won't be any voice announcement. When that happens, we know it must be smoke.UPDATE: I installed these detectors about a year and half ago. They are very, very sensitive. They've gone off twice so far. I'm pretty sure the first time was caused by trace amounts of smoke that entered the house from a fire far away. I could barely smell it, but only outside. I don't know what caused it the second time, but I suspect it was dust because there's a lot of air movement in the room where the alarm was triggered.SECOND UPDATE: The detector that was giving me false alarms is next to a door that tends to accumulate a lot of dust due to the way the HVAC system moves air through the house. The detector is right in the stream of air that leaks around the door when it's closed. I started cleaning the dust of the doorframe and door edges once every few months, and I haven't had a false alarm since then.