Abstract: A circuit for resetting a computer upon detection of changes in the signals of an RS-232C communications port in the computer. The changes may indicate an incoming phone call or loss of a previously established communication link. The circuit may monitor the RING INDICATE (RI) signal of the RS-232C port to detect the former condition and either the DATA CARRIER DETECT (DCD) signal or the DATA SET READY (DSR) signal of the RS-232C port to detect the latter condition. A timer prevents spurious changes in the monitored signal from causing the computer to reset.