Might work, might not. If someone keeps their cell phone silenced in their pocket, unless you're strip searching you won't know it's there. Does the customer have some app on it listening to the environment and using some kind of voice identification to figure out who's there. Do you have smart TVs up on the walls at this place, because hell, they're probably monitoring you too.
And that's only for cell phones. We are coming to the age where there is no such thing as an inanimate object. Anything could end up being a spying device feeding data back to some corporation.
> Does the customer have some app on it listening to the environment and using some kind of voice identification to figure out who's there.
This is no different from "So-and-so joined the group, but is secretly an FBI informer!" sort of problems, in practice. It's fairly low on my list of things to be concerned about, but as offline groups grow and are then, of course, talked about by a compliant media as "Your neighbor's firepit nights could be plotting terrorist activities because they don't have cell phones!" when prompted, it's a thing to be aware of.
Though you don't need a strip search. A decent NLJD (non-linear junction detector) or thermal imager should do it if you cared.
I'm more interested in creating (re-creating?) the norms where, when you're in a group of people interacting in person, cell phones are off, out of earshot. It's possibly a bit more paranoid than needed, but the path of consumer tech is certainly in that direction, and even non-technical people are creeped out by things like "I talked to a friend about this, and now I'm seeing ads for it..." - it may be just noticing it since you talked about it recently (buy a green car, suddenly everyone drives green cars), or you may be predictable in ways that the advertising companies have figured out, but it's not a hard sell to get quite a few people to believe that their phones are listening. And, hell, I sure can't prove they aren't listening.
> Do you have smart TVs up on the walls at this place...
I mean, I don't. But, yes, those are a concern too.
And, yes. Literally everything can be listening. It's quite a concern, and I think the only sane solution, at this point, is to reject just about all of that more and more. Desktop computers without microphones, cell phones that can be powered off, and flat out turning off wireless on a regular basis (the papers on "identifying where and what everyone is doing in a house by their impacts on a wifi signal" remain disturbing reads).
I really don't have any answers. The past 30 years of tech have led to a place I do not like, and I am not at all comfortable with. But it's now the default way that a lot of our society interacts, and it's going to be a hard sell to change that. I just do what I can within my bounds, and I've noticed that while I don't feel my position has changed substantially in the past decade or so (if anything, I've gotten further out of the center and over to the slightly paranoid edge of the bell curve), it's a lot more crowded where I stand, and there are certain issues where I'm rather surprisingly in the center of the bell curve as of late.
And that's only for cell phones. We are coming to the age where there is no such thing as an inanimate object. Anything could end up being a spying device feeding data back to some corporation.