How to see if the magnetic entrance guard is on?

1, the reed switch is always open. When there were no magnets nearby, two small iron pieces left. When the magnet approaches, two small iron pieces are attracted together.

2. Look at the circuit diagram below: the circuit is installed on the door frame, and a magnet is pressed on the door near the reed switch. In this way, when the door is closed, the reed switch is attracted by the magnet and the light does not light up. After opening the door, the reed switch is turned off and the light is on. Where r is a protection resistor for protecting the power supply,