Call-In Switch, Momentary closure Staff station call-in to control center or administrator, Flush or surface mounting in standard outlet boxes, Heavy-duty long-life switches, Color-coded connecting leads for easy installation, The CA17 is a momentary push-button switch which does not incorporate SCR circuitry. It is designed for annunciator call-in in PI35A, SI35A, and Multi-Graphic systems that are equipped with the SCR25A module.