Nikon D5100 Reference Manual page 7

Choose how long the camera will remain before cancelling the
currently selected remote control release mode and restoring
the previously selected release mode (_ 37). Choose shorter
times for longer battery life.
Choose the pitch (High or Low) of the beep that sounds when the camera focuses
using single-servo AF (AF-S or when single-servo AF is selected for AF-A; _ 39), when
focus locks in live view, while the release timer is counting down in self-timer and
delayed remote release modes (_ 37), and when a photograph is taken in quick-
response remote mode (_ 37). Select Off to prevent the beep from sounding. Note
that a beep will not sound in quiet-shutter release mode (mode 1-_; _ 35).
The current setting is shown in the information display: .1_ is
displayed when the beep is on, (_ when it is off.
Select On to display ISO sensitivity in the viewfinder in place of
the number of exposures remaining.
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