This is a basic Voltage Detection Sensor module to measure the voltage across two terminals. The module operates in 5V and can measure voltage from 0V to 25V using a potential divider circuit. A pair of high precession resistors form a voltage divider circuit which converts the input 0-25V to 0-5V on the output pin of the sensor. This 0-5V can then be measured by a microcontroller like Arduino.