DK-DPU The Hybrex DK-DPU-1 doorphone is, as can be seen, a standard one button door phone. Designed for the Hybrex Gx series telephone system and IP gateway series systems it is a digital device running on a single pair from the main equipment and has relay contacts to control a door lock solenoid. The compelling feature of the DK-DPU-1, apart from its use of current digital technology, is that it is weatherproof. Built in a cast aluminum case with a silver-grey hammer tone enamel finish, the componentry of this door phone is gasketed and sealed against the ingress of moisture, for many years trouble free service.