How to Check if User input is from Barcode Scanner or Keyboard?

You could monitor the time it took for the code to be entered. A reader would enter the code much faster than a human typing it in.

If you have the possibility to modify the scanner configuration you can add some prefix/suffix to the scanned data. Then in the code you can detect those added characters.

If you can't, then only way is Ahmed's - measuring the time of data entry.

It is relatively easy done with RAW Input API.

Take a look at "Distinguishing Barcode Scanners from the Keyboard in WinForms"

I have a program that reads 3 different USB scanners and redirects the input to 3 different "channels" for processing. The code is somewhat extensive, so I am not postin it here. If you wish, I can paste some chunks of it or send you the project in e-mail.

As a clue are the imports:

#region Raw Input API

[DllImport( "User32.dll" )]
extern static uint GetRawInputDeviceList( IntPtr pRawInputDeviceList, ref uint uiNumDevices, uint cbSize );

[DllImport( "User32.dll" )]
extern static uint GetRawInputDeviceInfo( IntPtr hDevice, uint uiCommand, IntPtr pData, ref uint pcbSize );

[DllImport( "User32.dll" )]
extern static bool RegisterRawInputDevices( RAWINPUTDEVICE[ ] pRawInputDevice, uint uiNumDevices, uint cbSize );

[DllImport( "User32.dll" )]
extern static uint GetRawInputData( IntPtr hRawInput, uint uiCommand, IntPtr pData, ref uint pcbSize, uint cbSizeHeader );

#endregion

After you add the InputDevice to your project, you can listen to events by:

// Create a new InputDevice object and register InputDevice KeyPressed event handler.
input_dev = new InputDevice( Handle );
input_dev.KeyPressed += new InputDevice.DeviceEventHandler( m_KeyPressed );

The event handler m_KeyPressed lets you to distinguish your devices through e.Keyboard.SubClass

private void m_KeyPressed( object sender, InputDevice.KeyControlEventArgs e )
{
    // e.Keyboard.SubClass tells you where from the event came.
    // e.Keyboard.key gives you the input data.
}

Hope to have helped.