Round Voltage Meter - 6V-30VCompact size allows for installation in a variety of locations - the same round size as a standard 12V receptacle. For interior or fully protected locations only. Specifications:. Type: Round Digital Voltage Meter. 4V-30V DC. WARNING: This product can expose you to chemicals which are known to the State of California to cause cancer, birth defects or other reproductive harm. For more information go to P65Warnings.ca.gov.