If you are interested in monitoring computer COM port, there are many software alternatives. These applications can help electronic enthusiasts to monitor serial input/output data. We will discuss the best free and paid serial monitoring programs and investigate their pros and cons.
Eltima Serial Port Monitor
Eltima Serial Port Monitor is a software application that allows reading and recording RS232 port data going through your computer’s COM ports.

There are Standard, Professional and Company editions of Serial Port Monitor, starting from $99 USD.
Vovsoft Serial Port Monitor
Serial Port Monitor is a simple to use application that allows monitoring computer COM port data traffic. It is provided as both portable and installer editions. This software can read data from any COM port and send data to any COM port. You can change connection parameters such as baud rate (bits per second), parity, data bits and stop bits. This utility can send and receive data in ASCII text. Hexadecimal, decimal, octal and binary formats are also supported when displaying received data. Sending text periodically is possible, you can change the interval in milliseconds.

It is free to try. Perpetual license costs $15 USD.
EVMsoft RS232 Monitor
EVMsoft RS232 Monitor is a serial port software for building data acquisition applications, transfer data with devices connected to serial port by rs232 protocol. It can send and receive data in ASCII text, decimal, hexadecimal (HEX), binary, float (IEEE 754) format and any byte order. It can send file to serial port, send data periodically, and save data to file.

The license costs 9.75$ USD.
SerialMon
SerialMon is a RS232 serial port monitor/sniffer software for Windows. It is a free protocol analyzer for ABB RP570, ABB SPA-bus and NMEA 0183 protocol. It monitors RS232 communication thru software or with simple hardware. Its filesize is very small.

Provided as freeware.