How would you detect when something is removed from a box in the easiest way?

Hello,

I am trying to find a way to detect when stock is removed and need restocking. We use standard tip out bins like this one https://www.pinterest.com/pin/229683649723562923/

I'm scratching my head at the moment...

How would you detect when something is removed from a box in the easiest way? Pressure sensor?

Would love to heard what you think.

Thanks. Vincent

What type of items are in the bins? It is not going to be easy if they are small parts.

Weedpharma

They range from small plasters to small screws.

Any idea how I could solve this problem? Massive thanks