There are two products that are designed for similar purposes: however they implement different architecture and offer slightly different features. The two products are Serial Port Monitor ActiveX and Serial Port Sniffer ActiveX Controls. Both of these products are used to monitor the traffic between two serial ports, however Serial Port Monitor ActiveX supersedes the older SPS ActiveX Control, has better serial port monitoring engine and works faster and more stable. Unlike Serial Port Sniffer ActiveX (which creates virtual serial port with the same name as the port you are sniffing and redirects data between real and virtual serial ports), Serial Port Monitor ActiveX directly intercepts the data flow that passed through the serial port being sniffed. Excluding this redundant chain (virtual to serial) makes Serial Port Monitor ActiveX more usable and robust component.

Below is the detailed list of provided features:

SPM ActiveX
SPS ActiveX
Change DTR++
Change DSR++
Change RTS++
Change CTS++
Open/Close port++
Change Baudrate++
Change Handflow control++
Change Line control++
Detect Ring++
Write to port++
Read from port++
Change control chars+(OnIrp)
On/Off break+ (OnIrp)
Read data substitution+
Write data substitution+
Exact events timestamps+
Read 6 KB of data, while baudrate is 9600 (sec)610
Stop sniffing when port is opened+
Start sniffing when port is opened+
Trace the application that opened port++