Murphy's Law Sue it had to be the last one you checked because you thought it was disabled.
I have that sort (beep when the battery is failing) but the ones my mum has are a newer type that beep every now and then, to let you know they are working. Daft idea to my mind, as you could go days before you realize they've stopped beeping because they need a new battery and they wouldn't then be able to do the job they're meant for.

Jan