IMPORTANT NOTE: When reading the question below, keep in mind that Maryland law defines a "smoke alarm" as "single or multiple station device ... including a built-in internal alarm [siren]" and a "smoke detector" as "device tied to a ... household fire warning panel."

I am working on replacing smoke detectors in a single-family dwelling that was built in 2006, since the current detectors are all starting to fail (and are of an age at which they should be replaced anyway).

Maryland Code Public Safety § 9-104 says that this building should have had:

Smoke alarms [that are] alternating current (AC) primary electric powered units with battery backup or an approved alternate secondary power source

However, when I take the existing units down, I see that each one has unused 120V AC wires behind it but is actually completely battery powered.

Based on the dates of manufacture of the detectors, it appears that around 2010 the interconnected wired alarms that were originally installed were replaced with wireless detectors that communicate with a DSC SCW9057-433 alarm keypad that was installed in addition to the main burglar alarm unit. To make things more complicated, the main alarm (an HAI/Leviton OmniPro II) also has six Interlogix TX-6010-01-1 (PDF) wireless smoke detectors connected to it. Effectively, this means the first floor, half the basement, and one room of the second floor are monitored by the OmniPro, while the rest of the basement, second, and third floors are monitored by the DSC.

With the DSC system dead and the OmniPro no longer supported by the manufacturer, we are having both systems replaced by an Elk M1 Gold system, so I want to take the opportunity to get the smoke detectors done better (and also add Carbon Monoxide detectors, which the existing system does not have connected).

As I understand the law, it was theoretically allowed to replace the hardwired alarms with wireless detectors because they communicate back to an alarm panel. However, the law now requires all smoke alarms to either be hardwired or have a 10-year "long-life sealed non-replaceable" battery, and it is unclear from the text whether this applies to detectors too. (In an ideal world, I could run all-new low-voltage cable for hardwired detectors, which would definitely be compliant with the law, but that is far too expensive to consider right now.) In practice, this means the simplest solution is to install interconnected hardwired alarms using the original 120v wiring that exists in the building.

The problem is that I still want these alarms to signal the alarm monitoring company when they go off.

I found that Kidde makes relays (one for smoke and one for CO) that will trigger when the smoke/CO alarms go off. However, I also found that in the instructions for those relays, it says this:

CAUTION: The model SM120X/CO120X should not be used to connect groups of alarms to a fire alarm panel or to interconnect groups of fire/CO alarms together.

Residential alarms do not latch in the alarm condition and they are self-resetting. If an alarm connected to a module has the test button pushed or the alarm momentarily activates, it will activate the module for as long as the unit is in alarm. If more than one alarm is connected to the module and the module is tied to a control panel there will be no way of knowing which unit caused the alarm.

My initial reading of these paragraphs is that it explicitly discourages using the relay module for what I am trying to do, which leaves me with a multi-part question:

  1. Am I being too strict in my reading of the law, and it actually does allow me to install replaceable-battery detectors?
  2. If not, is there a better option for 120v hardwired detectors to communicate with an Elk alarm panel (either wired, via Elk wireless, or via Interlogix-compatible wireless)?
  3. Since the second paragraph of the Kidde manual quoted above seems to be explaining the reason they said the first paragraph, does that mean that I can install the relays anyway since I understand the downsides described but would rather have it than not have it?
  4. If I cannot do any of the above, would it be reasonable to only put in the bare minimum number of hardwired detectors needed to be compliant with the law and put wireless detectors everywhere else? (I really don't want to do this, but is it better than nothing?)

1 Answer 1


Smoke detectors are exempt from the sealed-battery requirement in Maryland law

Since smoke detectors are either powered by the central alarm panel's battery during an AC power failure or monitored for power failure and/or battery issues by the alarm panel in a wireless system, there's no reason for them to have a sealed battery. As a result, given the definitions in Maryland PSC 9-101(e) and (f):

(e) “Smoke alarm” means a single or multiple station device that detects visible or invisible products of combustion and includes a built–in internal alarm signal.

(f) “Smoke detector” means a system–connected smoke sensing device tied to a fire alarm control panel or a household fire warning panel.

, and that the sealed-battery requirement in Maryland law expressly exempts both system smoke detectors and centrally monitored wireless systems, anyway:

(a) This section does not apply to:

(1) a fire alarm, a smoke detector, a smoke alarm, or an ancillary component that is:

(i) electronically connected as a part of a listed centrally monitored or supervised alarm system; or

(ii) capable of sending and receiving notifications by:

  1. a low–power radio frequency wireless communication signal; or

  2. a wireless local area networking capability; or

(2) any other device that the State Fire Marshal designates as exempt through the regulatory process.

(b) On or after October 1, 2018, a person may not sell a battery operated smoke alarm in the State for compliance with this subtitle unless the smoke alarm is a sealed, tamper resistant unit incorporating a silence/hush button and using one or more long–life batteries.

, go ahead and install the wireless detectors you are planning on installing.

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