Canon EOS 20D Instruction Manual page 90

You can also silence the beeper
You can silence the beeper so it does not sound in any shooting mode.
_'_I Select [Beep].
_ Turn the <O> dial to select [a
Beep], then press < _ >.
i_ Select [Off].
_ Turn the <O> dial to select [Off],
then press <_>.
CF Card Reminder
This prevents shooting if there is no CF card in the camera. This can be
set in all shooting modes.
_ Select [Shoot w/o card].
_ Turn the <O> dial to select [1_
Shoot w/o card], then press <_>.
_ Select [Off].
_, Turn the <_> dial to select [Off],
then press <_>.
F_3
LiJ If [Off] has been set and you press the shutter button while there is no CF
card in the camera, "no CF' will be displayed in the viewfindar,
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