I don't know about your grocery store but the ones I've been to have maybe 5 on the shopping floor and probably a few more in the back. They all have physical controls which (I'm assuming) override the controller if something goes wrong. So if big bad hacker says "I'm gon' turn y'all fridges off if you don't pay me" it's not a threat, it's a silly joke.

Unless of course they turn it off without telling the businesses so the products go bad because nobody's watching over the weekend or smth. But then again, why would someone want to do that. I wonder.