The switch is actuated by the pull of a magnet as your finger would actuate a light switch. A "normally closed" switch is "on" until the maget opens the switch (to turn off the circuit).
This reed switch is normally closed so the meter reads the same as when the probes were touching. in Photo 2.
The magnet opens the circuit so the meter reads the same as when the probes were not touching in Photo 1.
