The standard WHS mobile device does not have an error sound when scanning an invalid bar code. The user may not realize the scan was invalid, which will likely cause some wasted time. Error sounds can be added to WHS if you have a clever programmer on hand to work on it. See below for instructions from Microsoft for this task.
Here is another link/video that discusses how to add error sounds to the mobile device portal.
http://organicax.com/2016/03/25/using-sound-as-feedback-on-the-warehouse-mobile-device/
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