Photograph a shelf label or your receipt. We read the prices, you check them, and they appear on the product pages as seen in that store.
The photo stays private and is deleted within 30 days; only the prices you publish are shown. On a receipt you may cover your tax number (NIF) and card digits: we read only product lines. See privacy.
Online prices: we read each chain's shop every day or two. The shading fills in quarters under 1, 2, 4 and 7 days; empty means we have not seen the price for over a week.
Prices seen in a store (from shoppers' photos and Open Prices) are seen once, so they drain more slowly: under 3, 7, 14 and 30 days; empty after a month.