When reed switch is opened, pin 2 of Arduino goes high with the help of the pull-up resistor R2, and the alert signal is available through the piezo-speaker PZ1 (not an active piezo-buzzer). At the ...

The Reed Switch Module project demonstrates how to detect the presence of a magnetic field using a reed switch with an Arduino Mega. When a magnet is close to the reed switch, it closes the circuit, ...

[Bryan]’s dog-fed detector uses a reed switch and an Arduino clone to detect when the lid is opened. When the reed switch goes, low, the Arduino lights up an LED.