Honeywell Xenon 1902HC Quick Start Manual page 8

Very Low Beeper (Nighttime Mode)
The following bar code silences the base, and sets the scanner for a
very low beep when reading bar codes. After scanning this code, the
base beep, base and scanner power up beep, and scanner linking
sounds are all silenced. When a bar code is scanned, the scanner
emits a very soft beep.
Nighttime Mode
Low Beeper (Daytime Mode)
Scan the following bar code to set all sounds to on, but at a low
volume. The scanner beep, base beep, base and scanner power up
beep, and scanner linking sounds are all set to low volume.
Daytime Mode