First Alert SMI105-AC, Interconnect Hardwire Smoke Alarm with 10-Year Battery Backup, 1-Pack

Built in long life battery means no need to replace and no need to try to shut up annoying chirping of dying battery at inconvenient hours. Unit fits plug in connector and bracket of older units. Meaning replacement installation is simple: twist off old one, pull electrical connector off old one, plug connector into same spot on replacement and twist on new one into original wall/ceiling bracket. Then pull out plastic battery tab to connect battery and activate unit. Multipacks are economical way to replace all units at once. Theoretically, units have a ten year life. Replacing all units at same time is easier than tracking life of individual units and ensures all are within operational window.

Easy to install. Make power is off before you begin. Remove old detector but leave the screws annd use those to attach the new one to the electrical box. If you need to use the included adapter go ahead and connect the white to white, black to black and orange to red. Then just connect the adapter to the new detector. Be sure to remove the clear plastic strip to activate the battery. NOTE. You don’t need to connect the orange to red if the detector is not going to be connected to communicate with other detectors.

Bought this smoke detector because, you know, fire safety is important… Apparently not important enough for me to install it in under 90 days. But hey — I had other things to do. Like reorganize the garage. Twice. And stare at it in the box on the kitchen counter like it was going to mount itself. Meanwhile, my wife spent three months walking past it like she was in a house made of dry hay and open flames. Every time the oven turned on, I got the look. You know the one — the “If the toaster sparks, we’re done” look. ⸻ 🔥 Smoke Detector Functionality Once I finally summoned the courage (and a step stool), this thing installed easily and worked like a champ. Tested it with the “toast test” and yep — she’s got lungs. Loud enough to wake the neighbors, the pets, and possibly the dead. I feel safer already. So does my marriage. ⸻ 💵 Value for Money Excellent. A small price to pay for not living in a potential fireball and regaining my wife’s trust. Honestly, I should’ve paid more just for the emotional damage I caused by procrastinating. ⸻ 🧰 Quality & Build Solid construction. Doesn’t feel cheap or flimsy. You can tell it’s built to detect danger, not just hang out on the ceiling for decoration. ⸻ 🔄 Ease of Replacement Swapping it in for the old detector was fast and painless. If only me actually doing it had been that easy. Seriously, it took longer to unwrap it than to install it — once I finally picked up a screwdriver. ⸻ 🧯 Final Thoughts: • Yes, it works great. • Yes, it’s loud, reliable, and makes us feel safe. • No, I can’t explain why it took me a whole fiscal quarter to install it. Wife’s happy. House didn’t burn down. Marriage survived. 10/10 would delay installation again (kidding, honey).

Fit the previous model. The pin configuration on the images are correct. So far so good. Let's see if this battery lasts and the sensor doesn't go first. I'm using those cleaning covers when I vacuum now. I'm giving it 4 stars for the install and being what was listed. Can speak to how it lasts yet.

They are working great with no problems

These are to replace current First Alert units that began having false alarms. The existing alarms had new batteries and had dust blown out with canned air. They are 6 years old so we're replacing them with these newer models with 10-year batteries. They were very simple to replace. We'll see how well they hold up.

Replaced older sensors. Worked well with no problems.

I bought 7 First Alert SMI105 AC Smoke Alarms to replace existing units that were past their 10 year service life (Oops) and which required battery replacement every 5 years. I was delighted to learn that these new units used the same wiring and mounting brackets as the old 9120B model. So it was just a matter of unscrewing and disconnecting the old unit and plugging its old electrical connector into the new unit and then twisting the new unit into the old mounting bracket on the ceiling. Then all that was left to do was to pull out the plastic tab to activate the built in 10 year battery and test the unit. (Did you get that? No replacing batteries during the life of the alarm? WOW!) The only difficulty I had was in getting 7 units that were recently recently manufactured. What is got was a pkg of 3 made on 8/5/25, another pkg of 3 made in 7/29/24 and 1 made on 11/20/24 in spite of asking for 7 made on a recent date. Still working on that. So 5 stars for the smoke alarm design. Not so many for following delivery instructions though.