Interconnect 120VAC smokes with alarm panel


Active Member
At risk of creating a firestorm, I wanted to post some of my recent findings about interconnecting 120VAC smokes with residential alarm systems. This has been discussed many times before in this forum, and the discussions always digress into a hissing match with no-one proving their point because the arguments have based upon assumptions, opinions, and hearsay instead of upon content from verifiable and reliable sources.

In the interest of getting to the bottom of this controversy in a scientific, polite, and constructive manner, I’d like to ask that you please join in on the discussion, but if do so, that you please use verifiable content and report the content source.

I will start with this:

From the National Fire Alarm and Signaling Code (NFPA72-2010) Handbook:* Installations that include the connection of single- or multiple-station alarms with other input or output devices shall be permitted. An open, ground fault or short circuit of the wiring connecting input or output devices to the single- or multiple-station alarms shall not prevent operation of each individual alarm.

A. Such input and output devices include, but are not limited to, relay modules, notification appliances, phone dialers, security control units, heat detectors, and manual fire alarm boxes.

Paragraph was modified for the 2010 edition to clarify that the intent is to permit the interconnection of smoke alarms with other input or output devices. The examples of input and output devices were moved to Annex A. Furthermore, the revised paragraph requires that a failure of the multiple-station interconnecting means not prevent single-station operation of the multiple-station alarms. This coincides with ANSI/UL 217, which requires a fault to allow alarms to operate as single-station alarms.

However, the manufacturers of multiple-station alarms such as GE (now UTC) and Kidde discourage such interconnections. GE offers no explanation. From the GE ESL 320A/350 Series Smoke Alarms
Installation Instructions:
The 320A/350 Series smoke alarms cannot be used in systems with control panels, pullstations, heat sensors, elevator recall, fire door release, etc.

I had assumed that their reasoning was because the UL evaluation of the unit did not include this interconnection. However, now I am not as sure about this assumption and this is why:

Kidde sells a relay which ties into the tandem circuit for the purpose of connection to additional notification appliances. They, also discourage the tie-in of an alarm panel. However, they offer an explanation, but I am not sure how valid their reasoning is. From the Kidde SM120X Relay/Power Supply Module Installation Instructions:
CAUTION: The model SM120X should not be used to connect groups of alarms to a fire alarm panel or to interconnect groups of fire 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.

This statement does not make sense to me. I thought all interconnected multiple-station smoke alarms had a means to identify the culprit detector.
Again from the GE 350 Installation manual:
When units are interconnected and one alarm activates, the LED on units sensing smoke lights steadily, and the LED on the others flashes every 4 seconds. This feature allows you to identify which alarms have detected smoke.

And from the Kidde Model PI2010 Smoke Alarm User’s Guide:
WHEN UNITS ARE INTERCONNECTED, only the red LED of the alarm “which senses the smoke” or “is being tested” (the originating unit) will flash rapidly. All other units in the interconnect system will sound an alarm but their red LED’s will NOT flash rapidly.

Now I have two questions for the group:

1. Does anyone have experience with the GE or Kidde multiple-station alarms? Can you identify the culprit alarm when one gets set off?

2. Why are the smoke alarm manufacturers discouraging interconnection to the alarm panel, while NFPA 72 encourages it? No unsubstantiated opinions please, we have already heard those… just the verifiable facts….
Avoiding the firestorm,

1. The manufacturer's instructions state exactly how they operate. The Kidde relay module provides the explanation of the HV smokes self reset, and most have the additional functionality of a hush button on them. No latching means other than the host panel attached to the relay/module. If the alarmed detector self resets prior to being identified, then no identifying means. Without taking a ride and testing a bunch of 120V detectors, based on past experiences and common install practices, I would suffice to say all 120V detectors self reset, and identifying means are limited and described by the manufacturer, with the caveat of the older detectors that exist out there that operate to whatever standard that existed at that time (I believe that smoke detectors in new construction was mandated in the early 80's since I can't locate proper documentation) and unfortunately, there's a lot of those obsolete and most likely, non-functional devices out there still installed.

2. I wouldn't say NFPA 72 encourages it, I'd call the more appropriate statement being allows it, however the specific operation of the system as an entirety is also prescribed within the entire reference. ar

Part of the equation is listing and testing of devices, however I would, without getting engineers on the phone and documentation in line, would say the detectors and modules are really intended for more stringent applications, such as ADA and hearing impaired installations, where auxillary equipment interfacing is far more common, such as strobes and bed thumpers.


Active Member
I have more fuel for the firestorm........

Author Al Columbo published a couple of articles in "Security Sales & Integration" a few years ago about this very topic. He calls this interconnecting relay an "ancillary relay". His conclusion about connecting 120VAC powered multiple-station smoke alarms to an alarm panel is this:
In conclusion, when smoke alarms on a job meet all the necessary code requirements and the AHJ will approve the system as a whole, adding the same manufacturer’s ancillary relay may be acceptable. However, ask the local AHJ before you do it.

He goes into all of the concerns we have already discussed, plus a couple more I hadn't thought of. This is good reading.....

You can read the entire article from June 2005 here.

Also, here is the original article published April 2005 which spurred him into publishing the second article.

A similar discussion in 2011 about this same topic in another forum is documented here. Pay particular attention to the post by whizkid3 on 2011-01-27. He makes a lot of good points.
In my area, I remember it being around '99/00, smokes to meet code were installed, however most of the times, and I remember a huge article in SDM as such, was the tandem ring meeting temp-3 coding really didn't exist, so multiple sirens/sounders tended to be installed as the norm, and many AHJ's here started carrying sound meters and measuring "at pillow height" within an install, so I believe the installs I walk into in my area of the country might be looked at a little tighter than other areas, and I have yet to see an AHJ up here sign off on the connection of 120V detectors to a panel via an ancilliary relay.

The big picture, IMHO, as spelled out within the second article, is a very slippery slope to be on. As I stated prior, code does not forbid it, nor does it endorse it, but the big thing is, myself as a pro, I would not want to open the door to connect a non-listed or very grey area device to a panel within my control, even with the AHJ's blessing. As I've stated before, just because it can be done, does not mean it is a good idea or should be done.

In the case of the third article, the posts cited are valid in respect to a commercial application vs. a residential application, and frankly, a lot of the commercial applications I work with have monitored points in addition to the unsupervised HV points that were pointed out, in stark contrast to a residence with a single system connected, with a lot more unsupervised wiring and devices.


Senior Member
The International Residency Code also permits the use of Smoke Detectors connected to a FACP in place of Smoke Alarms for a while now. Not sure which came first the IRC or the NFPA for this.

One theory I have heard (not saying this is a fact) is that people sometimes abandon a FACP when the cost of the monthly service becomes to great or the premise is sold. An interconnected Smoke Detector loop would still be active even if the FACP is no longer in service and would provide some level of protection (often the bare minimum).

So rather than force someone to choose a LV Smoke Alarm connected to a FACP in place of or in addition to Smoke Detectors that may already be in place the AHJ's can choose to permit the connection of the Smoke Detector loop to trip the FACP and dial the central station which is an added level of protection above and beyond the Smoke Detector loop required by code as the bare minimum protection for the premise.

Basically in previous threads some people stated it was against the NFPA etc to connect Smoke Detectors to a FACP which is a common but incorrect statement (not everyone can know every part of the code as it evolves). It is permitted (for whatever reasons) when accepted by the local AHJ. Some people may not agree with the concept and they dont have to choose the option if they are not comfortable with it just like an AHJ does not have to accept it even though the code does.


Active Member
I believe I have finally reached the root of this issue. I will explain my findings, but in order to prevent this from becoming a really, really long post, I will summarize as much as possible and paraphrase the code a bit. If you want to look up the code reference for more detail, it will be in brackets.

First, I must define some terms.

Notification Appliance - A fire alarm system component such as a bell, horn, speaker, light, or text display that provides audible, tactile, or visible outputs, or any combination thereof. [NFPA 72 3.3.113] A sounder is an example of a commonly used notification appliance.

Single Station Alarm – A detector that incorporates a sensor and an alarm notification appliance in one unit [NFPA 72 section 3.3.175].

Multiple Station Alarm - A single station alarm capable of being interconnected to one or more additional alarms so that the actuation of one causes the appropriate alarm signal to operate in all interconnected alarms [NFPA 72 section 3.3.104]. These alarms are normally powered directly by 120VAC building wiring and are also commonly known as “builder smokes”. The GE 320A/350 series smoke alarms are examples of multiple station alarms.

System Smoke Detector - These detectors are connected to and powered by a control panel and may also have integral notification appliances, depending on the model and manufacturer.[NFPA 72 section 11.7.2] The term “system” smoke detector is defined in ANSI/UL 268. These are also known as 2-wire and 4-wire smokes. System Sensor models 4WTA-B and 2WTA-B are examples of “system smokes”.

Household Fire Alarm System - A system of devices that uses a fire alarm control unit (panel) to produce an alarm signal in the household for the purpose of notifying the occupants of the presence of a fire so that they will evacuate the premises. [NFPA 72 section] The Elk M1 with system smokes is an example of a combination panel (burglary/fire) and a Household Fire Alarm System.

Now I will get into some of the requirements for smoke alarms in residential occupancies. Please realize that I will be talking about requirements for new construction in jurisdictions that have adopted the 2009 version of the International Residential Code (IRC). I believe this is case in a large majority of the state-wide and local jurisdictions in the US, but local codes vary. Please check with your local AHJ for proper guidance. Most jurisdictions in the US do not require adherence to the latest codes unless major modifications are made to the residence.

The IRC requires that smoke alarms be listed in accordance with UL 217 and installed in accordance with NFPA 72. [IRC section R314.1] UL 217, entitled “Single and Multiple Station Smoke Alarms” specifies the requirements for “builder smokes”. It does not cover requirements for “system” smoke detectors.

As an alternate, the IRC permits Household Fire Alarm Systems which are installed in accordance with NFPA 72. [IRC section R314.2] UL 268, “Standard for Smoke Detectors for Fire Protective Signaling Systems” specifies requirements for “system smokes”.

NFPA 72 requires that a complete fire alarm system shall be installed with either a set of multiple station alarms or with system smokes. However, once a complete system is installed, detectors of either type may be added as supplemental to the system. [NFPA 72 section 11.3.2]

NFPA 72 requires that multiple station alarms comply with UL 217. [NFPA 72 section 11.7.2]

NFPA 72 requires that system smoke detectors comply with UL 268. [NFPA 72 section 11.7.2]
Manufacturers of smoke alarms and system smokes certify their products to meet either UL 217 or UL 268, but not both.
The GE 350CX smoke alarms, the Kidde SM120X relays, and First Alert (BRK) RM4 relays are certified to meet UL 217, “Single and Multiple Station Smoke Alarms”. They are not designed meet UL 268, “Standard for Smoke Detectors for Fire Protective Signaling Systems”.
UL 217 specifies requirements for stand-alone and interconnected smoke alarms not connected to an alarm panel. If a smoke is connected to an alarm panel it must meet UL 268 instead of UL 217. There are two key provisions in UL 268 which the GE 250CX does not meet. These are:
1. ANSI/UL 268 requires that a means be incorporated to identify the initiation of an alarm remain activated after the smoke has dissipated from within the detector. [NFPA 72 section 7.5.2]
2. NFPA72 requires that household fire alarm system smoke detectors, initiating devices, and notification appliances be monitored for integrity so that the occurrence of a single open or single ground fault in the interconnection, which prevents normal operation of the interconnected devices, is indicated by a distinctive trouble signal. [NFPA 72 section] Monitoring of the tandem relay coil in the GE350CX is not provided and therefore does it not meet this requirement.
Because of these two items, the 350CX cannot be listed per UL 268, and therefore it is not recommended to be connected to an alarm panel per UL Standards.
I find it interesting that while UL 268 requires these two features, UL 217, for “builder smokes”, does not. With this difference, UL is setting the standards of integrity higher for a “household fire alarm system” than for “builder smokes”.
To continue this discussion, and In order to prevent confusion, I need to define a couple more terms:
Supervised: In the context of the remainder of this discussion, “supervised” is a term applied to wiring, meaning that there is a mechanism to detect certain types of failures in the wiring. End-of-line resistors are used to supervise wiring circuits. This practice is also called “monitored for integrity”, which is different from “monitored” as defined next.
Monitored: In the context of the remainder of this discussion, “monitored” is a term applied to household alarm systems, meaning that such a system can report alarm and trouble signals to a central monitoring station.
You may find it surprising that the 2006 IRC essentially banned household fire alarm systems. Look it up. [2006 IRC section R313.1] However, even more surprising, the 2009 IRC permitted their use again, but with the requirement that they be monitored. [2009 IRC section R314.2]. The 2012 IRC, which is not yet been adopted by many states, continues with this requirement for monitoring.
Suppose I want to bring my 21 year old system up to current code under IRC 2009. Because the way the codes are written, and with available hardware, I am forced to choose between either of two system designs. The first is to use builder smokes which are not supervised and cannot be monitored. The second is to use the household fire alarm system which is required to be supervised and monitored.
Let’s suppose I pick the Household Fire Alarm System, an ELK M1 with System Sensor smokes. When the day comes to sell my house, I can visualize an inspector telling a prospective buyer this: “This house has a Household Fire Alarm System. Building code requires a lifetime monitoring contract with “ATD” in this house.” Well, that would be more than enough to scare me off from purchasing.
So the idea of a household fire alarm system and required monitoring is out. Now I’m forced to choose the builder smokes. But I still want monitoring, just not required monitoring. I know…..I’ll just run a wire from this smoke relay to the alarm panel. The NEC and NFPA 72 allow it, but there is this issue with the manufacturer and the UL. The smoke relay is not UL listed for connecting to a household fire alarm system. It seems like a little ol’ wire won’t hurt anything.
But now when inspector comes around and says,”Uh-oh you have monitoring…UL says that is a no-no”. I can take care of the issue in about 5 seconds with a pair of wire- snippers. Problem solved - no more monitoring. Now I, the home buyer, the inspector, and the UL…we are all happy.


With all that being said, I have five recommendations concerning this issue:

1. I say you should always follow the recommendations of your local fire marshal.
2. I say you should always follow the recommendations of your local building inspectors.
3. I say you should always follow the manufacturer’s recommendations for device installation.
4. I say you should always use components UL-listed for the particular installation.
5. I say you should always do what I say and not what I do.


Active Member

UL does not require wiring integrity monitoring for “builder smokes”, but it does for smoke alarms connected to an alarm panel. The GE 350CX smoke alarm is UL listed as a “builder smoke” and is therefore not recommend to be connected to an alarm panel.


Why not supervise the 120v power at the end of the circuit? Just like you would with a 4-wire smoke circuit. Wouldn't this meet the requirement? You could wire the zone through a 120v relay and get a trouble signal when the power goes out. The problems I see would be nuisance troubles for short power outs and the biggest concern with this is that heads can be removed without any faults. Unlike system devices.
It seems that fire marshals and inspectors would embrace this method because many times it is the only practical solution to monitoring for fire.


Active Member
There is no requirement to wire 120VAC smokes in a daisy chain fashion like with 4-wire smokes, so you'd need an EOL relay at the end of each branch. Then you'd have to run a wire to each of those, so you have to have a 120VAC wire and then a 12v wire...a lot of wires.

But the real issue here is that coil of the relay that interconnects the smoke to the alarm system is not monitored. That function would have to be built into the smoke detector. A circuit to a 4-wire smoke has three states. 1. Closed circuit- meaning fire alarm, 2. open circuit- meaning trouble, and 3- EOL- meaning normal situation. If the manufacturer could open the circuit to the alarm panel when the coil of the relay goes bad, then you have it.
Why not supervise the 120v power at the end of the circuit? Just like you would with a 4-wire smoke circuit. Wouldn't this meet the requirement? You could wire the zone through a 120v relay and get a trouble signal when the power goes out. The problems I see would be nuisance troubles for short power outs and the biggest concern with this is that heads can be removed without any faults. Unlike system devices.
It seems that fire marshals and inspectors would embrace this method because many times it is the only practical solution to monitoring for fire.

Piper got this in his post, however as you alluded to, the wiring methods that most builder smokes are installed in would be a pigtailed connection, as that's how every one I've looked at being wired in the field. Also, how a LV install vs a HV install is accomplished is completely different in nature, and unfortunately, I've seen many HV installs where the EC tied the convenience outlets/lighting in a utility space to the fire alarm power and only carry the traveller to the detectors.


Active Member
A smoke detector is part of a "system". A smoke alarm is self contained, whether it single station or multi-station. Now that this is clear, what is a wireless smoke if I don't install the related panel?

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Active Member
That is a good point. I'm not sure of the answer to your question. Single station wireless smoke alarms can function as a single station alarm but also communicate to an alarm panel. If you don't install the panel, then it is a single station smoke alarm. If you install the panel and communicate to it, the it think it would still be considered a single station smoke alarm, but this situation would be very similar to interconnecting a wired smoke alarm to the panel. I think that UL 217 and UL268 only apply to wired smoke detectors/alarms, but now I have to check.


Active Member
GE (now UTC) certifies their wireless smoke alarms to UL 217, while Honeywell and DSC certifies to UL 268. Although interesting, this is really beside the point of this thread.