According to the official project page, the HAT and breakout both are built around a DE2120 scanner module. This component uses a camera to capture barcodes and uses image recognition to interpret the data. Om indicates the new boards can read up to 20 barcode symbologies including things like UPC and QR codes.
In addition to the barcode scanning features, the HAT also has a buzzer, button switch, and a status LED. The barcode HAT is designed to match the form factor of the Pico, measuring in at 26mm x 76mm.
To get a closer look at this project, check out the official Kickstarter and maybe pre-order one for yourself. Donations of $60.14 USD (£45) will receive a Barcode Scanner Breakout while $66.83 (£50) will secure a complete Barcode Scanner HAT board.