First Alert · Wiring adapter plug (old Kidde harness → First Alert / BRK alarm)

First Alert ADK-12 adapter: which Kidde plugs it fits, and which it doesn't

Also printed as: ADK

Quick answer

ADK is First Alert's (BRK's) adapter plug for putting one of its alarms on a ceiling that was wired for an older Kidde, Fyrnetics or Lifesaver alarm. Its guide limits it to the Kidde models it lists, made on or before January 1, 2004, and says it cannot connect Kidde CO alarms. Firex wiring needs a different plug, the ADF.

Last checked November 4, 2026

At a glance

What it does: It sits between the existing Kidde-family power connector in the ceiling and a listed BRK / First Alert alarm, so the house wiring does not have to be cut¹
Old alarms it fits: Only the Kidde / Fyrnetics / Lifesaver models in its guide: the 1235, 1275, 1285 series, 1276, PE120, PE120E, PI2000 and the HD135F heat alarm¹
Age limit on the old side: The guide says the plug can be used on those Kidde-family models made on or before January 1, 2004¹
New alarms it takes: The BRK / First Alert alarms its guide lists, including the 9120 series (ionization), 7010 series (photoelectric), SC9120B smoke + CO combo, HD6135FB heat alarm and an auxiliary relay¹
Kidde CO alarms: The guide says the ADK plug cannot be used to connect Kidde carbon monoxide alarms¹
Model not on the list?: The guide says an old Kidde-family alarm that isn't listed has to be taken out of the system, and shows a Kidde connector with round holes as one it cannot be used with¹
How many on one loop: No more than 18 units in total, of which at most 12 are smoke alarms¹
Space in the box: If the adapter and wiring won't fit in the junction box, the guide says to remove the old connector and fit a First Alert power connector instead¹
Electrical rating: 120 V AC, 100 mA maximum¹
Who should fit it: The guide calls for the power to be off at the breaker or fuse box first and says wiring and installation must be done by a licensed electrician¹

Replacing it

Firex wiring instead: For older Firex harnesses First Alert's guide uses the ADF plug, not the ADK. It too is limited to listed Firex models made on or before January 1, 2004, and cannot connect Firex CO alarms²
Newer Kidde alarms such as the i12040 and i12060: Those models are not on the ADK guide's list. Kidde's own 20-9003 adapter lists them for moving to a newer Kidde alarm instead³
After fitting it: Test each alarm one at a time and make sure every interconnected alarm sounds each time¹
Recalls: Search CPSC's recall list for your exact alarm models before reusing an old alarm on a new loop⁴

Related models

Other models that cite the same adapter

Each link goes to another model page that cites the same adapter document. Whether two alarms can share a plug is answered in that document, on the model page.

Common questions

Which old alarms does the First Alert ADK-12 fit?

Only the Kidde / Fyrnetics / Lifesaver models in its guide: the 1235, 1275, 1285 series, 1276, PE120, PE120E, PI2000 and the HD135F heat alarm¹

Can the First Alert ADK-12 connect a carbon monoxide alarm?

The guide says the ADK plug cannot be used to connect Kidde carbon monoxide alarms¹

Does the First Alert ADK-12 fit Firex wiring?

For older Firex harnesses First Alert's guide uses the ADF plug, not the ADK. It too is limited to listed Firex models made on or before January 1, 2004, and cannot connect Firex CO alarms²

Sources

First Alert / BRK — Installation of the ADK Adapter Plug (PDF) checked 2026-11-04
First Alert / BRK — Installation of the ADF Adapter Plug (PDF) checked 2026-11-04
Kidde — 20-9003 Wiring Adapter User Guide (PDF) checked 2026-11-04
CPSC — Recalls & Product Safety Warnings checked 2026-11-04

Facts are restated in our own words. If a source page changes, the "checked" date tells you how fresh our reading is. Spot something out of date? Open an issue on GitHub.

Published November 4, 2026. Part of the First Alert / BRK brand hub.