Industrial Desktop/Wall Mount Ring Down Telephone is a non-hazardous rated version of Guardian???s Zone 1 DTT-51-Z telephone. It has a Type 4X, IP66 weather rating without being housed in a separate enclosure. This unit has a few more standard features than our normal weather resistant units including a hands free speakerphone and a built-in ring detect relay. All DTT and DTR models can be wall mounted or used as a desk telephone.