What Replaces the BRK 4120B and 9120B, and Can BRK Replace Kidde?

Adapter PlugsThe Fire Alarm Supplier
BRK SMI100-AC hardwired interconnect smoke alarm with battery backup

Often, yes. First Alert / BRK sells adapter plugs (ADK-12 for Kidde, ADF-12 for FireX) that join a BRK alarm to the existing connector, but only for the alarm models listed on the adapter's instruction sheet. For the BRK 9120B, First Alert names the SMI100-AC as the replacement.

This guide covers 120 V hardwired household alarms. Turn the breaker off before touching the wiring; BRK's adapter instructions call for a licensed electrician, and installation has to follow the alarm's manual, NFPA 72 and your local code official.

What replaces the BRK 4120B, 9120B, SC9120B and 7010B?

First Alert and BRK publish a "replaces" line on their product pages for most legacy hardwired models:

Old model Replacement named by First Alert / BRK Type
9120B SMI100-AC Hardwired ionization smoke alarm, 9V battery backup
9120LBL SMI105-AC Hardwired ionization smoke alarm, 10-year battery backup
SC9120B SMICO100-AC Hardwired smoke and CO alarm, battery backup
SC9120LBL SMICO105-AC Hardwired smoke and CO alarm, 10-year battery backup
7010B, 7010BV SM100V-AC Hardwired photoelectric smoke alarm with voice alerts
SC7010BV SMCO100V-AC Hardwired photoelectric smoke and CO alarm with voice alerts
SC7010LBLV SMCO110V-AC Hardwired smoke and CO alarm, 10-year battery backup, voice alerts

The 4120B is the exception. BRK's support site lists the 4120, 4120B and 4120SB as obsolete and points owners to its replacement finder rather than to one model. BRK's adapter instructions group the 4120 and 9120 series together as its AC and AC/DC ionization alarms, and the SMI100-AC is the current alarm of that type. One caution: the SMI100-AC manual's list of alarms it can interconnect with includes the 9120 and 9120B but not the 4120B, so do not leave old 4120B units on the interconnect wire with new alarms. Replace the group.

BRK's own product page already shows a newer model number, SM6W01, as the direct replacement for SMI100-AC part numbers, so expect the model on the box to keep changing. Check the "replaces" line on the manufacturer's page for the alarm you are buying.

Do I need an adapter plug to put a First Alert / BRK alarm on Kidde or FireX wiring?

Yes, unless you cut off the old connector and wire in the First Alert one. The two adapters are:

Adapter Fits the connector of Kidde / FireX models listed on BRK's instruction sheet
ADK-12 Kidde, Fyrnetics, Lifesaver 1235, 1275 and 1285 series, 1276, PE120, PE120E, PI2000, HD135F heat alarm
ADF-12 FireX 406 (G-6), 4518 (ADC), 4618 (FADC), 5000 (FADC), 484 (PG-40), 4480 (PAD), 5700 (ADH) heat alarm, 499 relay

Both are sold in packs of 12. The instruction sheets set these limits:

  • The adapter cannot be used to connect Kidde or FireX carbon monoxide alarms.
  • The listed models are the only ones that may be interconnected through the adapter. An alarm that is not listed has to be removed from the system.
  • Each sheet shows connector shapes that are incompatible and states the adapter can be used on models manufactured on or before January 1, 2004. Compare your connector with the drawing before ordering.
  • If the adapter and wiring do not fit in the junction box, the old connector has to be replaced with a First Alert power connector.

First Alert's support pages add that Kidde and FireX used different plugs on older models and on CO alarms, so the adapter does not fit every model.

Can alarms from different brands be interconnected on the same circuit?

Only where the alarm's manual lists the other model. The SMI100-AC manual says to connect the alarm only to compatible units and lists First Alert and BRK smoke, smoke/CO and heat alarms and the RM4 relay. It lists no Kidde or FireX models. The limits are 18 interconnected units in total, no more than 12 of them smoke alarms, all on the same breaker, with less than 1,000 ft of interconnect wire.

The adapter sheets, dated 2007, do state that the BRK alarms of that period (4120 and 9120 series, 7010 series, SC9120B and others) are compatible with the Kidde and FireX models in the table above. They do not cover the current SMI and SMCO models. If you are moving to current First Alert / BRK alarms, the way to stay inside the manual is to replace every alarm on the interconnect wire at the same time.

Will the new alarm fit the old mounting bracket and plug?

Expect to change the bracket. First Alert says new alarms generally do not fit old mounting brackets and that screw-hole positions vary. The plug is usually the same: First Alert states that all current First Alert, Onelink and BRK alarms use the same wiring harness, and that an alarm less than about 20 years old probably has it. It still recommends changing the harness with the alarm, because a wiring fault can stay behind in an old one.

Hardwired, 10-year sealed battery or wireless interconnect: which do I need?

Replace like with like. Where the house has hardwired, interconnected alarms, install hardwired alarms with battery backup. The First Alert manual notes that new construction requires AC-powered, interconnected alarms, and that battery-only alarms do not interconnect.

  • Hardwired with battery backup: the SMI and SMCO "-AC" models above, or the SC5 hardwired smart alarm, whose manual lists the SMI100-AC, SM100V-AC, 9120B, 7010B, SMICO100-AC, SC7010BV and SC9120B as compatible.
  • 10-year sealed battery: for locations with no alarm wiring, for example the SMCO210. First Alert's feature list for it does not include interconnection.
  • Wireless interconnect: battery alarms that signal each other by radio, such as the SM500V, give interconnection without running a wire.

How do I tell when a smoke or CO alarm has reached end of life?

Read the date of manufacture on the back. First Alert says smoke and heat alarms should be replaced 10 years from that date, and CO and gas alarms after 5 to 7 years depending on the model. Current models also sound an end-of-life chirp. On the SMI100-AC it can be silenced for about two days at a time, and not at all once 14 days have passed since the first signal.

The store stocks the BRK and First Alert lines. For a whole building or a model not listed, request a quote.

Sources

Tags: Adapter plugs, Brk, First alert, Replacement guide, Smoke alarms