Security & Fire Protection Systems/Smoke Alarm & Security System Relationship?


Hi Dave,

My main question is:  How, if at all does my security system play a role with my smoke detectors?  More questions at the end.  Sorry for the length of this.

Itís time for me to replace/upgrade my smoke detectors (11 & 21 years old).  Ideally, Iíd like to have my 6 current smoke detectors all interconnected and add 1 or 2 more units.

I have multiple brands and types of detectors, interconnected and non-interconnected units and a security system that is disconnected.  Hereís what I have today:

3 Firex Model G-6 Ionization smoke detectors (interconnected)
1 BRK System Sensor Model 2400TH) photoelectronic detector (The LED is off.  No sound when testing the interconnected alarms.)
2 Lifesaver Smoke Detectors Model #1275 (NOT interconnected)
1 Gentex siren (does not go off when testing the interconnected alarms)
1 Ademco 4140XM security system that has been disconnected, disabled and battery removed, but most the wiring in place).

When I press the test button on one Firex alarm, all 3 Firex alarms ring at the same time.

Even though the LED is off, I thought the BRK System Sensor and Gentex siren might ring too because I see the 2400TH called out on the 4140XM schematic, but they didnít.  Maybe the power for these comes from the 4140XM?  In addition, the System Sensor is mounted less than 3 feet from 1 of the Firex alarms.

Ideally, I would like to splice into the 3 existing interconnected units to make a 6 or 7 unit zone.  I would use combo CO and Ionization Smoke Detectors Kiddie KN-COSM-IB, Combo Photoelectric and Ionization Kiddie PI2010 (as a replacement to the BRK sensor), and the basic smoke detector Kiddie I12020 or i12040.

I would remove the current BRK Sensor and Gentex Siren and repair the drywall.

What issues do you foresee with expanding the 3 alarm system to 7 alarm system?

Are the components I selected compatible with each other?  One unit has a Smart Hush feature; will that feature work only on that alarm or all the alarms?

Thank you for any advice.

Hello Ron, and thanks for your questions.

Sounds like you have three separate smoke detection systems. I'd suspect that the first was the combination burglar/fire system... and yes, the BRK 2400 is a model that connects to the control panel. This is a completely different situation from the standalone detection system that uses the Firex G-6's and the LifeSaver detectors.

So my supposition is that the original system was the combination burglary/fire system. When that was shut down, I'd guess that the three interconnected G-6's were installed to replace it.

I can't say whether the two LifeSaver detectors were a later add-on, or an attempt to replace other G-6's that failed at some time.

In order to bring things up-to-date (and up-to code#, you'll want all of your smoke detectors interconnected.

The two things you need to keep in mind are detector compatibility and wiring.

You're already on the compatibility thought... so here's a Firex?Kidde Compatibility chart that may be of help:

Now, this is geared more toward replacement compatibility, so once you decide which model you want, it's best to check the installation instructions to ensure that it's designed to work with any other detectors that remain. But since your detectors are pretty old already, I'd suggest that you purchase ALL new detectors. That'll eliminate any question on their compatibility.

The average useful life of smoke detectors is about ten years, and the manufacture date should be printed on the back of each detector.

The other issue is the electrical wiring... 120 volts AC, plus one conductor to interconnect the detectors. The trick is that for the interconnection feature to work, all the detectors must be on the same electrical circuit #same circuit breaker). So, you'll have to do some investigation there.

Finally, you asked about the Hush Feature. For interconnected detectors, the hush button should silence all of the alarms -- as long as it's the detector with the Hush Feature that initiated the alarm.

I hope this helps, and if I've left anything out, please write again.

Best Regards,


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Dave Neuweiler


The design and application of burglary and fire systems for homes and businesses. Helping alarm owners understand how their system works. Helping to troubleshoot false alarm problems. Questions about monitoring issues.


Over a quarter century in the industry. Experience in installation, service, and monitoring centers. Training manager for a national protective services company; director of education and training for a national trade organization for for alarm dealers.


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