This function returns an HRESULT value.

If the lock succeeded, S_OK is returned. Note that the return value does not confirm a device unlock. All other values indicate failure.

SHDeviceLockAndPrompt can only be called by a privileged application.

A successful return value does not guarantee that the device was unlocked by the user, or even successfully locked, but only that the process to lock and unlock the device has started.

Reference