Wow. I can't speak for the law in Thailand (where police surveillance is prevalent), and the law in Britain (London has surveillance cameras all over the place), but here in the United States, there is well-established law about the expectations of privacy (or lack thereof) in places that are open to the public -- places of public accommodation, like restaurants.
As a general rule (there are exceptions), if you're open to the public, you have no expectation of privacy in public
areas. However, there was a case many years ago in New York involving a restaurant called Le Mistral that had been cited for health code violations, and some TV journalists came into the restaurant during serving hours to do a followup story. They videotaped patrons as well as staff, but only in the public dining areas, not in the back or kitchens or employee-only areas. Some of the restaurant patrons were pretty upset about being filmed (the story goes that some of them were seated with people they shouldn't have been with -- you know, married, but not to each other) and the restaurant sued for, among other things, invasion of privacy. The TV station countered that the restaurant was open to the public, so there was no legitimate expectation of privacy. In an (as far as I know) unique ruling, the court said that it was open to the public, but only to members of the public who intended to purchase the restaurant's goods/services/food/drinks, which the TV station didn't intend to do. So essentially the court concluded that the journalists were trespassing. (This is an oversimplification, but I don't want to get too technical.)
But again, that case is an outlier. Some of our states have laws prohibiting the use of hidden cameras, but with the ubiquity of cellphone/tablet cameras, as well as the new device you're referencing, I think it is going to be harder and harder to argue that people have an expectation of privacy in public parts of places open to the public. The government is starting to argue that in the context of Fourth Amendment (unreasonable search and seizure) cases, and it is likely to seep over into civil actions as well.
Before people start saying, "But what about Food Lion?", that case did not involve a state that had a law prohibiting the use of hidden cameras. Rather, Food Lion's claims (which included counts not relevant here, such as fraud) turned on the ABC TV employees getting access to the back/prep parts of the store, where customers aren't allowed. If they'd stayed in the public part of the store, the outcome might have been different. And ultimately, the award of damages ABC had to pay to Food Lion was tiny -- about $1400 -- as compared to the original award of over $5 million.
(I'm well aware of the prohibitions some grocery stores place on photography within their premises; I'm not sure that those restrictions are legal, but to the extent they are, they'd probably be based on a copyright theory -- a copyright interest the store has in displays of fruit, vegetables, etc.)
Finally, law aside, there have been a lot of complaints on this site from Roadfooders who have been told not to take photos of their food at restaurants, which certainly puts a crimp in the wonderful trip reports and reviews we see on this site. Do you really want to discourage that kind of interaction with your patrons? Personally, if a restaurant employee started inquiring into the medical necessity of any device I was wearing, I'd be out of there -- and maybe considering filing a claim with the EEOC or local equivalent.