Twelve units. That is the number below which the espresso cups start to be a problem, because the supplier takes nine working days and you sell about one a day.
Most shops carry that number in someone's head. The stock system knows the count, but nobody looks at it until the shelf is empty and a customer asks.
The system watches the stock count in Shopify, WooCommerce, Square or Zettle every hour. Each product has a threshold, which you set once in a Google Sheet. The sheet also holds the supplier name, their order email and the usual case size.
When a product drops below its threshold two things happen. You get one message, on WhatsApp or by email, that says which product, how many are left and how fast it has been selling over the last four weeks. And a reorder email appears in your Gmail or Outlook drafts, addressed to the supplier, with the product code, the quantity rounded up to full cases and your account number.
You read it, change the quantity if you like, and press send. Or you delete it. The system never sends to a supplier on its own. If five products from the same supplier go low in the same week, they go into a single draft.
This is the kind of thing we build. It runs in your own accounts. What is sitting at zero on your shelves right now that the till knew about a week ago?