Some smoke detectors beep for a while after you change the batteries.
I had that happen to me a few weeks ago - turned out I’d replaced the batteries in the WRONG smoke alarm - it was a forgotten one that hadn’t even been up on the wall whose batteries had started to run down. (The same one that my landlord had been giving me grief over taking down and losing, so that I bought and installed a new one!! 
)
We had a similar thing happen to us a few months ago. The smoke alarm in a hall next to three bedrooms beeped. We replaced the battery, it didn’t stop. The beeping wasn’t constant so it was hard to tell where it came from. I unhooked all the smoke alarms and carried them around in a bag for a whole day. Still there was beeping in the hall that seemed to come from the bracket on the ceiling.
It drove us crazy for weeks. It turned out to be that the battery in the carbon monoxide detector was warn out and it was beeping. It was plugged into the wall outlet right below the smoke detector and hallway accoustics or just our expectations made us hear the sound as if it came from the ceiling.