Output voltage is not clearly marked on the board. This is only a problem if you order modules with different output voltages from this vendor. To tell that this is the 3.3V module, look for the tiny SMT resistor labeled 41C to the right of the 8-pin IC. If you actually look very carefully in the pictures provided, you will see it, but unless you know what you are looking for it may not occur to you to check that particular part!