Red digital voltage display ^^ Low E. S. R. (Equivalent Series Resistance) ^^ 16 V / 20 V surge ^^ Audible warning tone for reverse polarity ^^ Audible warning tone for low battery voltage ^^ Audible warning tone for voltage overload ^^ Use high performance 4GA or 8 GA OFC (oxygen free copper) cables for best results ^^ Sound Storm Laboratories offers a 1 year Platinum Online Dealer Warranty so long as the purchase is made through. We strongly encourage professional installation of this product to ensure proper and safe functionality