I have one of the higher end UPS from APC. On it I was able to disable the beeping. It does not alert me at all.
It is one that have the LCD screen on it that can tell you the number of events, current power usage and so on.
I agree the BEEPING is annoying as hell when it goes off in the middle the night.
edit:
I did some googling and it looks like you can use the Powercute software from APC and tell the APC to disable the audio beeping