The Videx 3021 handset with 12V A/C buzzer for use with VRDK kits and older Videx door entry systems. It has a plug in replaceable handset cord and lock release button. This model is compatible with older Videx systems using 3+n and 4+n (traditional) wiring. This handset does NOT have a small black call tone setting switch on the left hand side of the cradle – see Videx handset 3011 for electronic call tone handset.