I have been asked by a customer to interface to some old Protect emergency call systems, and I am trying to determine what protocol these things use to communicate with the central station. Does anyone have any ideas? At this point, I have not physically seen the systems so I don't know model numbers etc. All I know is that there are 3 vintages of system installed. I am guessing that it is some pulse format, but I don't know if it a 'standard' format or some proprietary format. Any help is appreciated.
John