Forms :: Text Box With Barcode Scanner

This question is related to a restaurant POS system design. Is there a way to allow a text field in a form to be filled by a scanner only, unless an event is triggered? Rather than using a magnetic strip ones for gift cards, we're thinking of using the bar code version. However, to prevent employees from fraudulently entering the six digit code, the code must be inputted by a scanner. We do also would like to allow user input with keyboard in case scanner malfunctioning, but would require a "manager" login first.