Originally Posted by ESpen36

If all you present is an ID (and no boarding pass with barcode), how does the "scanning" work?

I'm asking because I know many people, myself included, who use our passport or Global Entry, Nexus, or passport cards as ID at the checkpoints because we do not want to show an ID that includes our home address. These documents do not have barcodes, although they do have machine-readable strips (MRZs).