Hall Effect Sensor U18

From the shop's description

Hall Effect Sensor U18 is a high-quality electronic component designed for Arduino, prototyping, and educational electronics. A Hall effect latch works like a switch. It will latch on when the magnet is near the sensor (south pole). It will turn off if the opposite magnet pole (north pole) is applied. It can be used for counting rpm of rotating shaft or fan by putting 2 magnets with opposite poles after each others. It’s perfect for DIY makers, students, and anyone building custom electronic circuits or STEM kits.