The Voltage sensor can detect the supply voltage from 0.0245V to 25V. This module is based on resistor divider principle. This module allows the input voltage to reduce 5 times. As the Arduino or microcontroller analog input voltage is normally maximum 5V, the input voltage of this module can not exceed 5Vx5 which is 25V. If you give 25V DC to Vin, you will get 5V output in the 'Sig' pin.