detecting items being removed from a shelf

I have a small shelf that I put things on (think self-serve sales) and then over the course of time, the items are removed. Checking this all the time is not convenient, and I'd like to have a system to "notify" me when all the items are gone or when it's low. The notification is no problem, have plenty of ideas I can complete for that. The issue I'm noodling is how to "know" if everything is gone. I first thought I could do it with force sensitive resistors and so I bought some velostat thinking I could use that. I haven't gotten that to work well yet. I could try force sensitive resistors, but hate to pay the price for them without knowing they'll be stable long term so that when the items are removed, the reading will in fact meaningfully change even if the load as been the same for days and days or longer. A load cell could work I guess but then I'd need an amp and supporting bits...was hoping to avoid that. Anyone have any ideas? The shelf is enclosed by walls and a top, etc. I can modify it in any way I want since I totally own it. Thanks.

What's being on the shelves (ear rings or car batteries) will most likely determine the way you will detect if they are missing, so you might provide more info on that part.

Right! The shelf and the items won't ever weigh more than 10kg, and they'll be removed in increments of 250-500g (~8oz-1lb). Thanks.

if you look at any vending machine, or many shelves in stores, they have a pusher that pushes the product to the front.
put a HALL sensor and a magnet and presto ! empty shelf detection.

I did some code a year or so ago for a product which might be useful, you...
visit www.stockee.com.au, they do exactly what you’re planning - you may get some ideas from their kit.

It’s quite clever, and reliably measures chunky items down to small nuts & bolts.