I believe this is the worldwide smallest & most Convenient to use voltage meter, you can put it anywhere with this very handy display. This is the 2-wire version of the volt meter, the two wires are used to power the module itself and meanwhile measure the voltage     Simply connect the red wire to the positive supply, and black to negative ground. The display has a microcontroller STM8S003 that will read the voltage, compare it to a stable reference and display the voltage with 0.1V precision on a 3-digit 7-segment display. It works from 3.2V up to 30V so it will be good for nearly any electronic project! The meter draws 3-4mA to power the microcontroller and display. This particular LED display is  very readable. Mounting tabs make this module easy to attach to any box or plate.