Question 1

How do you silence this alarm? Apparently the low battery notification only starts after midnight and WILL NOT STOP unless you have another battery.

Accepted Answer

I am certain this applies to all brand and model of smoke detectors.  Once the low battery beep starts happening, which is always just as your falling off to sleep, there is only one way to stop it.  Follow the steps outlined below.
1 - put all weapons in your house under lock and key. (this is for the safety of you your family and the manufacturer of the smoke detectors).
2 - Give the key to someone you can trust and that your are not capable of overpowering.
3 - Find the smoke detector that is beeping. Tip, its never the one you are standing beneath look up at.
4 - Ice your foot because by now you have kicked several walls, doors and furniture.
5 - Assuming you have located the guilty smoke detector and have not yet burned down your home or found a way to access your weapons in step 1, move to step 6.
6 - Take the guilty smoke detector(s) into the garage and smash them into as many pieces as possible with the biggest hammer you own.
7 - Most likely you have stopped the regular beeping but every 20 to 40 minutes or so you will still hear a beep.
8 - Start a fire in the back yard fire pit and when the fire has reached white hot with glowing red hot coals put the smashed bits and pieces into the fire and let it burn until it burns out on its own.
9 - Take a shower and get dressed because by this time your late for work and haven't slept.
10 - When you get home that evening and hear another beep burn the house but make it look like an accident.

Question 2

Can a  BRK Model 92120B smoke detector directly plug in and replace an old BRK Model 4120B smoke detector (without an adapter)

Accepted Answer

Yes.  I just replaced 2 very old (older than 10 years) BRK Electronics Model 4120B smoke detectors with these newer First Alert/BRK Brand Model 9120B units.  My older units were yellowed with age, so I also replaced the plastic base.  I did reuse the 3 pin electrical connector, as the "old" electrical connector matches the new unit.  The new smoke detectors are functioning/self-testing normally.

Question 3

can these be connected together so if one is set off they  all go off?

Accepted Answer

Have these in my home. House was built about 4 years ago (2017) Came with the house.. One goes off they all go off. They are connected to each other by wire. I did have the one in my bedroom that I had to replace prematurely.  It was just going off for no reason setting the entire house alarms. It was easily identified by the light on it that it was the culprit. Basic troubleshooting taking out of system all was good. I am a 42 year volunteer firefighter,  held a Chief, Captain , Luitenant, Firefighter and other various positions . My opinion,  having them all wired together, so when one goes off they all do is SMART! Been to multiple house fires through all my years and seen where the families on the first floor watching TV while their second floor or basement is burning up. 🔥

Question 4

My entire home is equipped with BRK smoke detector (4120 B) and Carbon Monox Det (CO50120B). They need replacing. Will new BRK fit extant casings?

Accepted Answer

The mount screws will fit but the base plate itself is slightly smaller and you might have to touch up paint. The connectors will fit as well so no need to change those

ASIN	B07B4CG1PG
Best Sellers Rank	#222 in Tools & Home Improvement ( See Top 100 in Tools & Home Improvement ) #2 in Smoke Detectors & Fire Alarms
Brand	First Alert
Built-In Media	9-volt battery (3), First Alert BRK 9120B Hardwired Smoke Alarms with Battery Backup (3), Mounting brackets with hardware (3)
Color	White
Customer Reviews	4.7 out of 5 stars 4,630 Reviews
Global Trade Identification Number	00029054018489
Item Dimensions D x W x H	1.9"D x 5.6"W x 5.6"H
Item Type Name	Hardwired Smoke Alarm with Backup Battery
Item Weight	9.6 ounces
Manufacturer	First Alert
Mfr Part Number	9120BFF-3
Model Number	BRK 9120B-3
Number of Items	3
Power Source	Battery Powered,Hardwired
Product Dimensions	1.9"D x 5.6"W x 5.6"H
Product Style	Standard Detection
Sensor Type	Ionization
Style	Standard Detection
UPC	029054018489
Unit Count	3 Count

First Alert 9120B / SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, 3-Pack

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