An improved public intercom system is described which has a sealed enclosure including an extruded chassis having a front wall and a rear wall. The front wall has an interface panel and a viewing panel mounted within cutouts. A plurality of axially aligned module cover plates supporting system components are mounted over cutouts in the rear wall. The interface includes a speaker, a microphone, a call initiation means, and a camera positioned to acquire images of the area in front of the interface panel. One of the cover plates including an outer surface with heat dissipation protrusions, with a blower located on said rear wall being oriented to direct air across the protrusions to extract heat from the chassis interior. A two-way communication means is mounted on a module plate and programmed to initiate a call to a pre-programmed receiver responsive to a command from the call initiation means.