I can't start monitoring serial port which is already opened by other application
Serial Port Monitor is capable to Start/stop monitoring the serial port which is already opened by other application (available in Professional Edition only and in free demo version).
You are not able to open port if you are using Send Dialog function which is the lite version of terminal. Note that it is actually a built-in terminal, being a bonus feature in SPM. To know how to start new monitoring session, please visit the page: http://wiki.eltima.com/user-guides/serial-port-monitor/starting-session.html