I have a logoff trigger that trace my program logout.
If an user close correctly the program the trigger trace the logout.
If the program crash the logout isn't written.

The trigger (and table to write) is on sys.

CREATE OR REPLACE TRIGGER logoff_audit_trigger
BEFORE LOGOFF ON DATABASE
DECLARE
PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
update
   stats$user_log
set
   logoff_day = sysdate
where
   sys_context('USERENV','SESSIONID') = session_id;
update
   stats$user_log
set
   logoff_time = to_char(sysdate, 'hh24:mi:ss')
where
   sys_context('USERENV','SESSIONID') = session_id;
update
stats$user_log
set
elapsed_minutes =
round((logoff_day - logon_day)*1440)
where
sys_context('USERENV','SESSIONID') = session_id;
COMMIT;
END;
/