... in airports, industrial zones, government buildings, schools, hospitals, etc. hand-held metal detector MD-200 Features:1. Operating frequency:2. Weight ... of power 8. Battery: 9V battery (suitable for working for 40 hours normally)9. Control: circulation switch (On, Off, a ... alarm simultaneously13. Alkaline cell (7V-9V) can work over 40 hours and distance does not change14. Warn automatically when short ...