For USB devices, where you have access to both the device and some proprietary software that can drive it, this isn't so difficult: you can intercept the USB co

For USB devices, where you have access to both the device and some proprietary software that can drive it, this isn't so difficult: you can intercept the USB commands quite easily, then it's a matter of spotting patterns for each activity. For intercepting the USB traffic, you have a few options: - software USB Snooping; this hooks into your OS's USB subsystem and intercepts data. The Linux USB debug stuff works well for this, I've had less luck on Windows. - using a virtual machine and forwarding it the USB device. I've had success with this for intercepting the USB traffic for a device with only proprietary Windows drivers, but where snooping in Windows directly failed. Boot up in Linux, set up a Windows virtual machine, forward the USB device to the VM, install the Windows drivers in the VM and use Linux' USB debug interface. - Hardware USB snooping devices. You physically insert them between your USB device and the PC, and they log the data flowing through. Obviously, this is a bit more expensive, but will basically always work.