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I have been battling with this problem for weeks. Fire Department changed batteries and still have alarms go off on occasion. Just had them come again because one of them started to have a blinking red light. BRK Electronics, Model 4120B, 120 VAC, 60HZ

Can I buy a replacement at Home Depot of Lowes??

Samr problem. This has happened on several occasiions, always at night and usually 2 or 3 am!!! The only way to stop it was by disconnecting ALL the alarms. I eventually found one of the alarms would continue to go off periodically when disconnected, and am replacing it. I will let you know if it works.

I have BRK Electronics mod. 4120B, hardwired smoke alarms (9). The battery is difficult to change, the doors get stuck and jam. They are terribly made. I have broken(accidently) the door release trying to change battery. They also tend to chirp when you do get new batteries in. They should be replaced by company. They are there to protect my family, I have no faith in these smoke alarms help?
Richard Bernal California 93012

Model 4120B is a discontinued model number. Doesnt have to do anything with replacing batteries since the americium-241in the unit is depleted, thus making the alarm sound or chirp telling the homeowner to replace. The new model to purchase is the model 9120B. This will last another 10 years before having to be replaced. Check link for purchasing information

We're having the same alarm problem. we dusted the alarms and changed the batteries and they are still alarming.

all of our alarms started to go off today, thinking there was a fire i was running through the house checking each room, garage, attic, crawl space, water heater room and outside thinking it was picking up smoke from somewhere. No fire though, did anyone contact the company for replacements or did you guys just go out and buy new alarms? Thank you for any help

Mine were going of briefly every hour. Replaced batteries, but that only made it more frequent. Had to find the one that triggered first. removed battery, but it chirped if left plugged in. Removed from ceiling and kept pushing test button to drain the capacitor. Replaced the next morning. Thanks to "solution" about the depleated Americium-241, makes sense

I have had the same problem and disconnected them all. Does the 9120b fit into the electrical clip that was used on the 4120b?

I have the same problem and disconnected. Does the 9120b fit into the electrical clip that was used on the 4120b

Our smoke detector is making a chirpping sound once every minute. We've disconnected the unit from its "house" and it seems like the chirpping is coming from the wiring!? Does that mean we must replace the whole thing? Wires and all? Please help.

4120b's replacemet 9120 should fit into same base based on my reaserach. I will try in few days. Will order today