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Security & Fire Protection Systems/Only 3 of my 5 brand new interconnected smoke alarms work!


Hi Dave,

I'm hoping you can help me with an issue after finding this forum. My 5 interconnected smoke alarms were 10 years old, so I've replaced them all with the comparable replacement model. They are all 5 Kidde i4618 models. There is one in each of the hallways of my 3 floors plus 1 each in each of the 2 3rd floor bedrooms for a total of 5. I first installed the 2 3rd floor bedroom ones yesterday. They both went off when I tested each alarm separately. Then I installed the 3 hall ones today. All 5 show the periodic flashing red light and steady green to show they are working from battery backup and electric current. Yes, now the 3 in the halls all will go off together when tested separately but not the 2 in the 3rd floor bedrooms. I'm at a loss. I called the Kidde technical service today and was advised to test the wiring in the house to rule that out as an issue. I followed the advice of using an extra 9 volt battery to do this by putting red to positive and white to negative for each of the 3rd bedroom smoke alarms. Both alarms work with all the rest going off when I test them individually like this by disconnecting the wiring to do so. The Kidde rep said the 3-cord harness from the ceiling wires to the plug in the alarm might be bad so to replace it. I did in one of them. That didn't help. I'm at a total loss at this point as to how to proceed. The home was built 10 years ago. The circuit breaker looks fine to me. I read that the 3rd floor bedroom outlets and the smoke detectors should all be on one arc-fault protected circuit. And that appears to be the case in my breaker box. I hired an inspector for 2 inspections of my home before buyng it, and it passed both of them with no mention of any issues with the interconnected smoke detectors. What should I do to get the 2 bedroom alarms to go off all together with the other 3 in the halls that already speak to each other as they should? Thanks for any help you can provide!


Hello Rick, and thanks for writing.

I suspect that all of the detectors are not on the same electrical circuit. I think you'll find that the pair upstairs that work correctly are on one circuit, and the other three are on a different circuit.

You can test this theory by turning off the circuit breaker that powers the detectors, and then inspecting the AC light on all five.

If it turns out that all 5 ARE on a single circuit, please let me know, and I'll work out a test to investigate further.

I hope this helps!

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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