Abstract: A programmable data alarm containing a dedicated microprocessor serially interfaced with a data communications network is configured to monitor the network's data transmission lines for transmission of preselected characters. A number of preselected character strings may be input into the data alarm through data terminals coupled to the communications network and stored in a non-volatile memory. The microprocessor compares each character string transmitted over the communications network to the stored preselected character strings and outputs an audible and visual alarm signal when a match between the transmitted and stored strings occurs. The microprocessor may also be configured to monitor the handshake lines of the data communications network for signal transitions that will trigger the alarm signal.