Sony ICD-ST20 - Manual (Page 15)

Basic Operations
15 GB
Memory remain indication
During recording, the remaining memory indicator decreases one by one.
When the remaining recording time reaches 5 minutes, the remaining
memory indication flashes.
When the remaining time reaches 1 minute, the remaining time indication
will flash in the display window regardless of the display mode (page 26).
When the memory is full, recording automatically stops and “FULL” will
be displayed with an alarm sound. To continue recording, first erase some
of the messages (page 35).
Note
When you set the BEEP (page 53) to OFF, an alarm sound (beep) does not
sound.