As mentioned in "How long can a USB flash drive last?", we should never pull the usb flash drive out of the USB port while it is still in operation. In Windows system, we shall always right click the usb drive and select "Eject", before removing it from your computer.
Why is that necessary?
In theory, it's to ensure that Windows isn't busy reading from or writing to the drive when you remove it, something that could result in corrupted data or even a damaged drive.
BUT, what if Windows keeps saying it isn't safe to do so because "This device is currently in use"?
Windows becomes very unhelpful on this point, and won't bother to tell you what is actually using the device. Without that information, it's tough for a normal computer user to know how to fix the problem. Close all of your Windows Explorer windows, along with any programs that might be holding onto a file from the usb drive. Then try the "Safely Remove" option again. If this doesn't work, many of us may choose to restart the computer, which will always work but take a much longer time and interrupt your workflow.
There are many articles out there telling you it's perfectly safe to just ignore the annoying message from Windows and simply unplug your usb drive. But we won't advise you to do so, especially when you do have important data stored in your usb drive.
For more than ten years, we have been using a FREE software Unlocker to help with this situation. Your can safely download it from the PC Advisor website. The file size of this freeware is only 798 kb, which is much smaller than most of the photos nowadays.
This software reveals which of Windows' process are currently use the files stored in your usb drive, then give you the option to kill the process in question and unlock the file. There is no need to restart Windows, so in just a few clicks you can overcome the obstacle that was preventing you from safely removing your usb device.