Disconnected anti-theft alarm circuit using reed switch

It uses a reed switch KR to control the conduction of the thyristor
V, and uses a multivibrator composed of a 555 time base integrated circuit as an alarm generator.
    When the door is closed, the permanent magnet is close to the reed switch KR, the reed switch contact with a normally closed contact is disconnected, and the thyristor V is closed - no alarm. When the door is pried open, the magnet leaves KR and V conducts, which triggers an alarm.