what's the best way to detect the magnet? Use anther magnet. But it's not sensitive enough. You have to feel it by youself.Right！This Hall sensor knows whether there is a magnetic object nearby or not. And it correctly tells you through ditigal output.See below picture for a quick demo! 
Note: It's a omnipolar magnet dectector so that it can not tell two polarities apart.

Specification:

• Supply Voltage: 3.3V to 5V
• Indicator LED on board
• Interface: Digital
• Size:22x30mm (0.87x1.18")

Documents:

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  Product Includes:

  • Hall Sensor X1
  • cable X1