I think the OP might be mixing up serial-bridges with the actual bridged serial devices. E.g. FTDI-bridges have a Vendor-ID, Product-ID pair which can be used to identify bridged serial devices, if you assign special values. However, only their proprietary drivers (d2xx) allow enumerating the bridges attached to the PC. So there is no cross-platform or even a cross-vendor way to do that. However, if you know that your devices are FTDI-bridges and you happen to work on OS's with driver support, then you can bypass the virtual serial ports alltogether and identify/enumerate/communicate with the devices (I'm not too sure if the d2xx-drivers hand out handles that you can use with the usual OS file API though)."vendor id, product id "What's that ?I mean for a serial device. If they are present in the device protocol then fine, but that depends on the individual devices and their protocols.You can check whether there has been any traffic, which might be useful, but serial connections are just streams of bytes.