What’s the best way to detect the magnet? Use anther magnet. But it’s not sensitive enough. You have to feel it by yourself. This Hall sensor knows whether there is a magnetic object nearby or not, and it correctly tells you through a digital output.
Note: It’s a omnipolar magnet dectector so that it can not tell two polarities apart.

Connection Example – I/O Expansion Shield V7

Specifications

• Supply Voltage: 3.3V to 5V
• Indicator LED on board
• Interface: Digital
• Size: 22 x 30mm

Resources

• Wiki Doc
• DataSheet
• Schematics

Package Contents

• 1x Hall Sensor
• 1x Cable