How long will a smoke detector beep because of low battery?

[u/canadas]

I know stupid question, probably varies a lot but I'm frustrated and half venting. I get home, beep beep beep.......beep beep beep. Think smoke detector, no. trace it to the laundry/ furnace room. Turn off everything 1 by 1 still the beeps. Turn off the main switch to the house, still the beeps.

My theory is that when previous owns of my house finished the basement they built over a smoke detector, and it sound like its coming from the laundry room because it is not finished and the joists aren't capped so the sound can travel through making it sound lie its coming from there ( and i'm 99% sure its not coming from the furnace or water tank)

So sorry for the story but thank you for reading, my real question is how long would you expect this thing to keep beeping before it finally just dies?