How do you inspect hardwired connected detectors?

I’ve had a rash of finding hardwired detectors where the interconnect wire is incorrectly installed.
(And, a fair number of battery alarms found in a hardwired spot).

How do you verify that hardwired detectors connect to each other? When I press the button on such a detector, the beeping is so non-specific in location, I generally can’t make heads of tails of which detectors alarmed and which ones remained silent.

I’ve had the residents on occasion close a door and verify the connection, but this is not a universal solution.

A few systems, like the Kidde P4010DCS-W will give a detector count, but most do not.

It kind of depends on the house and the way it lays out. Most times I trigger the upper-level hallway and wait to hear the echo. I might hit a couple others if I don’t think they all sounded. In Oregon we have a real estate transfer law that detectors need to be <10 years so I often find myself pulling one or two to check dates. The handyman/homeowner special of installing battery powered units in place of hardwired is super common and I actually get a lot of pushback from said handyman or homeowner when they get busted. The other one I see a lot is just sticking new battery units next to the old/hardwired units.

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Our state law provides that hardwired smoke alarms can not be replaced with battery only units. That’s the most common thing I write up for home inspections. Curiously there is no requirment to replace units older than ten years for a real estate transaction but there is for rental licensing in some counties. Testing units for interconnection is hit or miss, so I usually don’t test it. County licensing for rentals does require all units to be from the same manufacturer to insure interconnectivity. That suggests to me that there may be a different signal from different manufacturers or even models as some are wirelessly interconnected these days.

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I wonder if you pull the back up battery from a single unit if that wouldn’t cause them all to chirp. Just make sure you put it back before leaving.

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FYI: Kidde and First Alert detectors are mostly interchangeable with regard to interconnect in practice. Both publish a list of the other’s detectors that they certify as interoperable.
The actual signal is low voltage, even on a hardwire unit, to account for power failure operation.

What really sucks are the “10 year” units. Don’t get me started on how many of those I’ve called out as detective (because of the way my business works, I replace them, and have to dispose of them by the bucket every few months).

County isn’t very interested in facts. When they require same manufacturer it becomes a big liability to deviate from their requirements. When you inspect for a municipality just do it their way or don’t do it at all. The low voltage thing is fairly obvious because they operate just fine on a 9 volt battery. I wonder if the wired interconnection just needs a ground to trigger. Try that sometime. If you actually disconnect the trigger wire, the unit your at won’t blast in your ear

The trigger is the 3rd traveler wire (usually yellow or red). There are some wireless interconnected systems that are pretty cool as well. Here’s a blog I wrote about them:

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Any other ideas?
Trained bats maybe?

Nice blog. Thanks for sharing.

I don’t test alarms. First the test button only verifies the batteries and siren works and doesn’t test the electronic smoke sensor. Second anything electronic may stop working before you leave the driveway. I only recommend they add them if none is found, recommend additional if too few are found and recommend they test them the day they move in and on a monthly basis. They will live in the house and it’s their responsibility to maintain them. If the house burns down don’t call me.


Keep in mind, older homes may not be interconnected, unless they have installed the wireless ones.

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Me either.


As Randy said these devices are smoke alarms not smoke detectors. Detectors are initiation devices that send a signal to an alarm panel. I know that we tend to use the terms interchangeably but they’re not the same.


Wouldn’t the smoke alarms have sensors in them that detect smoke?


Interesting, I test all that I can. One house, built in 2000, I tested a few weeks ago had older smoke alarms on the main level and zero functioned. The recently finished basement had newer smoke alarms, when I tested the first one all the basement ones went off. Indicating they were interconnected. The basement alarms were not interconnected to the main level.

I’ve heard from multiple realtors that in Colorado smoke alarms must be functioning for a house to be listed on the MLS. Now that clearly doesn’t always happen. But realtors are always quick to jump on those for an item that needs to be addressed.

Yes just like a smoke detector would. The difference being that the smoke detector will be silent and will send a signal to a fire alarm panel. The smoke alarm will sound an audible alarm and if it’s an interconnected type it will signal the other smoke alarms to provide an audible alarm as well.

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I understand the difference and was being a little facetious in the question. Mainly based on the reason the word “detector” being commonly used in the audible alarms.

I mostly don’t test smoke alarms/detectors and have a standard disclaimer as to the reason and explain why in my report. I do test new construction systems.

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Interesting, I test all that I can

I absolutely test every detector and detector/alarm I can. Frankly it has a user operable button just like a toilet we’re supposed to flush and a faucet we’re supposed to turn. I even carry a can of fake smoke for commercial inspections. Fake CO is available too, but it’s expensive and hard to use.

My question to other inspectors was how to test residential connected alarms, given the difficult noise environment.

I often recommend wireless alarm especially when there’s a crawl space full of gas equipment and no chance the smoke detector down there would be heard by anyone. I carry boxes and boxes of them with me to jobs, and often install the " X-Sense XS01-WR" model, after having disappointing results with Kidde and First Alert battery life on their lifetime battery models.

Earplugs are an inexpensive way to still hear the alarm and protect your ears.


Do provide this as courtesy to your clients?