A3144 Hall Effect Sensor as the name suggests works with the principle of hall-effect and is used to detect magnets. Each side of the sensor can detect one particular pole. It can also be easily interfaced with a microcontroller since it works on transistor logic. So if you are looking for a sensor to detect magnet for measuring speed of a moving object or just to detect objects then this sensor might be the perfect choice for your project.
How to use Hall-effect sensor:
There are A3144 Hall Effect Sensor one which gives an analog output and the other which gives a digital output. A3144 is a digital output hall sensor, meaning if it detects a magnet the output will go low else the output will remain high. It is also mandatory to use a pull-up resistor as shown to keep the output high when no magnet is detected.