Open device name using CreateFile
Here is a good explanation by Tim Robinson, MVP (Windows SDK):
Names of the form
\Device\xxxare internal NT object manager names which are inaccessible to Win32. You will only be able to access your device if it creates a symbolic link to\Device\MyDevicefrom the\??\directory. Objects in the\??\kernel directory show up through\\.\in Win32. Use Winobj in the DDK (or download it from www.sysinternals.com) to check.
NOTE: Nowadays NT namespace root is exposed via GLOBALROOT symbolic link, so any NT path is accessible to Win32 including \Device\xxx: use \\.\GLOBALROOT\Device\xxx. A device symlink is not required in such case.