If the scale is built into the shelf, how will it cope with my dinner last night? I took out the butter, left-over ham from Sunday lunch, leftover roast peppers (from ditto), eggs, fruit juice and cheese. Only the butter, fruit juice and cheese went back in, as the ham and 2 eggs disappeared into the pot.
How can it work out from all that change what's going on? As happens the cheese is dangerously low, so will need replenishing next shop.
I was cooking. I was in a hurry, and hungry. I grabbed everything I needed in one go, it all went back in the fridge together quickly, when my carbonara was cooked - to minimise time between serving and eating. I don't want to faff with a scanner and touchscreen in either of those circumstances.
I can see an online shopping tablet app working with RFID tags containing sell-by dates, plus past sales data, being able to help populate your shopping list. But to be honest, I don't see it being all that useful, because it would be so hard to train. None of the people I know eat the same 7 meals per week, and most of them buy what's on offer, or looks interesting, when they shop.
So all we're really talking about is keeping up with staple foods. Of which my fridge contains ketchup, salad dressing (of varying types), condiments, cheese (again of various types depending on what I'll be doing with it and season), milk, fruit juice, limes, eggs and veg (of various types). In my store cupboard there's spices (hard to track as they're used in such small quantities), oils and sauces (worcestershire, soy etc.), which aren't easy to track. Then finally you've got things like baked beans, tinned tomatoes, potatoes, pasta, rice. Of which only the tins can be tracked without trouble.
So for my fridge (and to be fair freezer) staples, this might save me 10-20 seconds a week. Out of the 30-60 seconds I spend before I go shopping, checking what I need. Well I'll pay £10 extra on a fridge for that, as long as it takes no more than 10 minutes to set up, and is likely to work, be easy to use, and not make the fridge more unreliable. That's not a compelling proposal.
I'm thinking of going to online shopping. But that makes this even less attractive. As I'll be doing that on my iPad, in my kitchen. Where it is but the work of seconds to open the fridge door, and look.