Listen utilizes standard Windows COM port drivers to tap into RS-232 transmit signals for monitoring bi-directional communications between two devices. Two COM ports are used in the listening device, the receive line of each connected to the transmit line of one of the communicating devices, (in parallel with the original receiver). Character data is captured and displayed in real-time. Data is displayed in the color and font specified for the particular COM port on which it was received. Binary data, not represented by a printable character, may be displayed in a variety of formats including bracketed decimal, octal, hex, or binary representations. In addition, each bit pattern may be overridden with a custom character string for display.