Remotely programmable equipment monitoring telephone line protocol

A master data processor (18) may send data indicative of equipment condition through a modem (24) to a modem (26) of a data processor (28) in a local monitoring center (over telephone lines) whenever they occur in response to a seize mode (59) or between established times of day (64, 68, 69), or whenever the telephone line becomes free (65)if the data messages amount to alarm conditions (65). Calls can be received at the local monitoring center 14 between said preestablished times (79-82) after a predetermined number of rings (83, 85).