There should be an app that handles the direction of sound / echolocation of the one smoke detector that is beeping "low battery". Doesn't seem to be one.

I’ve often wondered why they just don’t put a low battery light/led on the detector?

You could just use a battery tester on each unit?

I’d think you’d have to start with some sort of Wi-Fi connected “smart” smoke/fire detector. It’s likely it would report such. I had a Nest Home that was smoke/carbon monoxide/fire and it would push notifications to my phone for battery status. You could also identify with a button on the app and it would light it up like a Christmas tree.

most detectors have an LED that indicates its status.

OMG!! Just a few weeks ago I narrowed it down to the garage. Replaced both of their batteries. Still chirping. WTF. I took one down and brought it inside. Chirping still in garage. Brought other one in and still chirping in the garage. I blow them both out with compressed air. Dust and a moth come out. Replaced both batteries again with batteries from a new package. Still chirping. So I brought them both inside and the chirping is still in the garage. WTF!!!

Well….

About 6 months ago my wife the realtor replaced a detector at a house she was selling. She put the old one in a bag and placed it on a shelf in the garage. She meant to toss it out but forgot. I hate the damn chirping!!!

We currently have ADT for a security system in the house and the non wired detectors are obviously wireless with batteries. Some time last year there was an update and now the panel beeps (always between 2 and 4 am), but at least I can shut it up and go back to sleep. When I wake up, i can go to the panel it will tell me which detector needs a battery, with a number. Now, if only the installer numbered each detector, instead of just most of them...
With this tech, you would think they could program the beep to not go off until 6 or 7 am

Our detector is hard wired,, if the backup battery in one is bad it’ll chirp for a minute by itself then all the others will chime in.

I have switched to networked smoke alarms that show the battery status on a control dashboard.

Before that, I had a list of smoke alarm locations and would install new batteries every fall when the clocks were set to EST. Overkill? Maybe. But I never needed to get up at 3:00 AM to find the beeping smoke alarm.