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

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.

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

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.

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

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. 🔥

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?

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

Brand	First Alert
Style	9120BFF
Power Source	Battery Powered
Color	White
Product Dimensions	5.6"D x 5.6"W x 2.2"H
Item Weight	0.05 Pounds
Alarm	Audible
Operating Humidity	10-95% RH
Sensor Type	Ionization
Global Trade Identification Number	00029054015327
Number of Items	1
Manufacturer	First Alert
UPC	029054015327
Part Number	9120BFF
Item Weight	0.8 ounces
Item model number	9120B
Batteries	1 9V batteries required. (included)
Is Discontinued By Manufacturer	No
Size	1-Pack
Pattern	Filter
Voltage	120 Volts
Item Package Quantity	1
Number Of Pieces	1
Type of Bulb	LED
Cutting Diameter	5.6 Inches
Included Components	smoke detector, batteries, mount
Batteries Included?	Yes
Batteries Required?	Yes
Battery Cell Type	Alkaline
Warranty Description	10 Year Limited
Assembled Diameter	5.6 Inches

BRK First Alert 9120BFF/ SMI100-AC Smoke Detector, Hardwired Alarm with Battery Backup, White, 1-Pack

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