Unthinkable in today's Fire Prevention World but City's and Towns had an Unsupervised circuit to fire panels up till 1980s

A look back into the history of  fire reporting systems 

It was called a Candella Circuit and it was very unique when it came to monitoring fire alarms  basically it was a board with lights that lighted up when a contact on Fire Panel closed and it was used well into late 1980's  by the City of Pittsburgh  as well as other city's and towns . There was no supervision and you had no idea if wiring was even working until you did monthly building test.

Pittsburgh put the Candella Circuits in place when it got rid of the old Gamewell Master Box system  which was supervised and would work despite multiple wire breaks on the circuit how ever it was expensive to maintain a private wiring system in the city where Bell Telephone maintained and charged for using the Candella System It worked well and many fire alarm systems back then where not fully suervised like they are today .

https://news.google.com/newspapers?nid=1129&dat=19861107&id=UNM0AAAAIBAJ&sjid=4m0DAAAAIBAJ&pg=3284,1840806

https://news.google.com/newspapers?nid=1129&dat=19870706&id=udZRAAAAIBAJ&sjid=IW4DAAAAIBAJ&pg=6616,1669209

  The city would replace the Candella with a fully supervised technology called Derived Channel System in late 80's which sent special  sub audible tones back and forth over phone lines you could not hear to do the supervision. Bell Telephone called it REACT System

https://www.google.com/patents/US4868859

 But it only lasted a few years again due to the high cost of maintaining it and poor quality of phone lines in many areas at the time  and was turned over to Guardian Protection who eventually abandoned it.
Finally Fire Alarms where allowed to report in via Digital Dialer which used POT or Plain old Telephone Lines  which at first there where only 3UL Listed  central stations permitted to send signals to city which was Honeywell, ADT and Guardian Protection . But then the city of Pittsburgh finally allowed all centrals to receive and send signals to them in early 90's. All in All it was a learning curve for Fire Officials as technology and codes are constantly changing and facing the massive amount of Fire and Burglar Alarms the city has they did a good job administering them. Bottom line they kept Pittsburgh Citizens safe

Amazingly even thou the Candella system was unsupervised there where No incidents where it did not work that I know of  because Bell Telephone Employees did an excellent Job in maintaining and checking the lines   . Which where marked with special red caps anywhere they terminated.Unlike today where Verizon is trying to get out of hardwired or POTS phone lines

Of course today there are many ways to send in Fire Alarm signals from Digital Dialer's over POTS to Cellular and Internet Communicators and even Private 2 way radio