We purchased a home about a year ago that had three hard-wired smoke detectors installed. All of them were BRK Electronics Model 2002RAC. All have a 9-volt battery backup. They attach directly to three wires coming out of the ceiling using a connector plug that is on the end of the wires.
We believe they all were ionization-type detectors.

We had no problems with this system until about two months ago when the smoke detector on the top floor, where the bedrooms are located, began chirping randomly. It would chirp loudly, with the chirps spaced 10 to 15 seconds apart, for at least three to six times and then it would be silent. This often happened in the middle of the night, waking the entire household including our young child.

We replaced the battery but the problem just continued to get worse, with the random beeping starting to occur at all times of the day and night.

We decided that, perhaps, the smoke detector just needed to be replaced. We did not know how long it had been there but the house was 22 years old.

We could not find another BRK hard-wire with battery backup in our area. We had a still-in-box smoke detector/CO detector on our basement shelf that we had not installed in our old house, so we decided to use that. It is a Kitty Nighthawk KN-COSM-B. It is battery-powered only, not hard-wired, and we used a brand new battery. We believe it also is an ionization-type detector.

The random chirp began happening again within a day or so of putting in the new detector. We replaced the battery with yet another new battery. Yet, the chirp continues. Many times, the chirping happens when we have windows open, but not always.

Last night the chirping woke us all up again at 3 a.m. and my husband yanked the smoke detector off the ceiling. To our amazement, the chirping continued - apparently coming from the wires and connector dangling from the ceiling with no alarm attached to them.
We thought at first that we must be hearing things wrong and that the chirping must be coming from the smoke detector on the first floor. But we stood right under that gaping hole in the ceiling with the dangling wires and it was beeping at us.

Can someone help us? What is going on here? How do we stop this? The beeping is driving us nuts, depriving us of sleep, and forcing us to go without a smoke detector on the sleeping floor of the house in order to keep our sanity.

How can things keep beeping when no smoke alarm is there? Is it feasible for the wires and connector themselves to be emitting a beep?

Any insight, help, fix-it advice would be appreciated.

Thank you.

I could not find an obvious way to edit my post and I need to make a couple of corrections/clarifications.

First, it looks like our original BRK smoke detector was a photoelectric detector, not an ionization detector. Our current detector, a Kiddie Nighthawk (spelled Kiddie wrong the first time) is an ionization detector.

Second, does the housing up in the ceiling that holds the wires for the detector have a speaker or amplifier in it that is allowing us to hear the beep when no detector is connected?

We have a theory and would appreciate any feedback:
The original BRK detector was old and went bad, somehow losing its connection to the other detectors in the house and so causing the periodic chirping. Please note, the chirping never has been continual.
We put a battery operated detector up there and that does not stop the chirping because it is not connected to the wires, so the system still detects an interrupted connection somewhere and chirps.

Is this possibly our issue? If so, will finding another BRK hard-wired detector and putting it up there solve the problem?

Thank you everyone.

No way can the wires/connector make the sound.

And I don't know of any normal installation that would include anything else in or around the box.

I suspect that the sound is something completely different. Something in the attic and it is "coming though" the box as it is penatration into the otherwise "sealed" ceiling.

Go into the attic and check it out.

Also get some foam in a can seal the back side of the box.

And look around and see if there is anything around the box. The previous owner might have installed something else. Maybe a home rigged alarm for an open garage door or somethign like that.

But the main too things that I can think of would be a bad bearing on a wind turbine roof vent. Or a it you have HVAC equipment in the attic a bad bearing on the fan or fan motor.

Either one will make "somewhat" random sqeaking/chirping sounds.

Lets us know what you find.

Look for a smoke detector that has been installed in the attic. Take it out, you do not need one there.

Find the breaker that controls the detectors and turn it off. See if the chirping continues. If so, look for a bad turbine bearing, bird nest, other critter nest.

Thank you to both replies so far to my post.

I wanted to note that when I say the detector is chirping, I mean a loud, abrupt beep. This is not a sweet chirp that a bird might make or even a bad bearing on a mechanical system. This is the kind of beep that is shrill and loud that smoke detectors emit to wake you up. But instead of a continuous "beep, beep, beep, beep" that you get when there is smoke detected, it's just a single "beep," then silence for 10 to 15 seconds, then another "beep." This is a beep that can be heard all over the house and is loud enough that it has awakend us in the middle of the night.
It is similar to the kind of periodic beep you hear when the battery is dying in the detector. But, as I explained in my original post, we know it is not the battery.

We are going to make another run through the attic to check for a smoke detector up there, but we've never seen one.

We have no mechanicals up there either except for a radon system fan which is at the other end of the house, not right above where the smoke detector is located. Also, if the radon fan begins to fail even a little bit, its performance gauge drops and the performance gauge is right on target so the fan is operating normally.

Next time the beep sounds, we'll go for the breaker first to see if it stops the beep. If it doesn't we'll know it is coming from something else other than the smoke detector system.

Thanks all.

We are having the identical problem in our house in the same location and did the same trying to fix it(new battery, new smoke detector one with hard wiring one with battery alone).

No effect.

I guess it is temperature related. When the temp drops at night the battery voltage drops and the electronics may pick up on it.

We are going to put the battery operated one in the fridge tonight to check.

Maybe a call to the manufacturer is i order.

Has anyone come up with an answer to this problem? My grandson has a almost new house and has the same problem.