This interruption in the circuit causes the pen on the inking register at the central station to rise and make a mark on the already moving tape. The inking register which responses to a certain box is obviously the one connected to the circuit to which that box is connected. He starts the Police radio transmitter and announces the box number twice. If the fire apparatus has to cross Market Street, the traffic warning bells are sounded for a period of from two to five minutes. The control desk for the fire radio is also located at the Central Fire Alarm Station, but due to the high frequencies used in this two way ratio, its transmitter is located on the side of Twin Peaks.
Fire companies receive the reports of fires by means of the fire alarm bells in the fire houses.
Sometimes, however, the various chiefs are away from the fire houses and they are notified of a fire by means of this high frequency radio. Since both the chief's autos and the central station are all on the same broadcast frequency, a two way conversation can take place between the cars and headquarters, between headquarters and cars, or among the various cars that are in service. Ground tests are made for each box circuit at the end of each box test. The crew also records all box tests and directs the work of clearing box circuit troubles. Test signals are sent out over the system three times daily.