500
Some Walmart employees say customers are getting hostile at self-checkout — and they blame anti-theft tech
(www.businessinsider.com)
This is a most excellent place for technology news and articles.
It's not like you're trapped... you can just walk out if you want, but doing so without paying and carrying full bags may raise an eyebrow with employees. Although I think I could easily get away with that in my small village supermarket during quiet hours when nobody is paying attention.