How to check idle sessions over a threshold in Oracle

LAST_CALL_ET is the number of seconds since the session last called into the server. Filtering INACTIVE user sessions above a threshold surfaces dead connections that are still holding a slot.

ACCEPT p_min_idle_sec NUMBER PROMPT 'Idle threshold in seconds (e.g. 3600): '

SELECT sid, serial#, username, machine, program, osuser,
       status, last_call_et AS idle_sec,
       ROUND(last_call_et / 60, 1) AS idle_min,
       logon_time
FROM   v$session
WHERE  type   = 'USER'
AND    status = 'INACTIVE'
AND    last_call_et > &&p_min_idle_sec
ORDER BY last_call_et DESC;