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

The 10 year battery is great. Don't have to change batteries twice a year. Works well

I bought these to replace two old smoke detectors that were hard wired. The I installed the new base. The existing plug fit perfectly. I tested them to make sure when one alerted, the other one would alert as well. Worked as expected.

These were easy to connect to each other and easy to install! They were a great value especially compared to the other ones! Quality appears good. Tested them out and everything functions as it should. No issues with alarms going off for no reason. They should keep everyone safe, which was our main concern! I would buy these again!

Purchased 4 SMI105-AC (smoke) and 2 SMICO105-AC (combo CO & smoke). Replaced the existing 9120B and the SC9120B. I left all base plates in place and new smokes fit just like the old. However, the new combos simply did not fit and ultimately I had to switch to the new base plates. The appearance of the old and new plates is incredibly close. (See pic) but the size is about 1/16" different and its enough to prevent the new combo detector from attaching to the existing plate. I'm guessing that the combo was farmed out to some other company to make and the difference in size comes from a different manufacture's equipment.

When our home was built in 2016, the installed 6 First Alert # 9120's. One of the failed this month. I ordered 6 First Alert # SMI105-AC's as replacements, as they came with a ten year battery.Installation was quick as I only needed to twist, unplug the old ones, then snap these in. Both the mounting bases & wiring was identical. These also have a strong GREEN LED light to indicate the are functioning which is very easy to see, especially at night. (Had no idea which one of the old ones had failed so at 4 am I was climbing up the ladder the check each one until I found the culprit!)Very satisfied.

I had the basic smoke detectors by the same manufacturer. Every time we opened the (clean) oven the detector nearest the oven would go off. This one filters out those false alarms! In our town the fire department installs or changed batteries free. Prevents ladder falls which are their most frequent calls. Check your fire department. They may do the same.

These smoke alarms are great. I bought them to replace the 10 year old SMI100-AC and they were delivered to me overnight the next morning. They were so compatible they actually fit into the same as the old one. Freed the battery, plugged in AC and twisted into place.I was tired of being prompted to change 9 volt batteries every 6 months or so in the middle of the night. These replacements have 10 year batteries built-in, so that should not be a problem.My only complaint is against the product picker at the Amazon warehouse. I had ordered 3 of these and one of them was a basic SMI100. It requires a battery and doesn't connect to power. I promptly returned it and ordered another one that should come tomorrow morning.

Had to replace the original detector. It is a perfect size fit. Same design as original item. Great value for the money. It does work well on test mode.