In a shop the fastest search is the one with no typing: point the camera at the pack and get the prices. The Barcode Lighthouse on LowPrice's island is the screen that does it, and its job is to be quick and dull.
A scan returns a number, and the number has to become a product. The app asks the catalog for that code and goes straight to the product page when there is one match. When the code is unknown it says so and offers search with the code prefilled, instead of a dead end. A scanner that reads the same code thirty times a second also needs a rule: the first good read stops the camera and everything after it is ignored.
Permissions are most of the experience. The first time, a short sentence explains why the camera is needed before the system asks. If the answer is no, the screen offers the search box and a link to the settings. Every path ends at the same product page, where the price of each chain, per kilo, is waiting.