What does it show up as?

If it's just a storage drive you can check the file list on, that's easiest.

But if it's some special hardware device that doesn't show up as a drive letter you'd need to use RegisterDeviceNotification/WM_DEVICECHANGE to detect DBT_DEVICEARRIVAL notifications for the devinterface class GUID giving you the specific device type like smart cards, security devices, sensors, etc.