This is the state of the bell.

Value	Meaning
0	Ring indefinitely
255	Don't ring
N	Ring for N calls

Read-only by automatics.

Write/read-write by in_permitted_area, ring_bell, event_wake_up, event_go_to_roll_call, event_go_to_breakfast_time, event_breakfast_time, event_go_to_exercise_time, event_exercise_time, event_go_to_time_for_bed, searchlight_caught, solitary, guards_follow_suspicious_character, event_roll_call.