Using "DMZ" in this context is very confusing, in common usage it means the exact opposite of what you intended.
A lot of home routers have a "DMZ" feature that gives the device you put in the DMZ full access to the outside internet, but restricts their access to other hosts on the local network.
It's typically used for gaming machines when you can't be bothered to forward a lot of ports individually, I have a gaming console in a "DMZ" on my network so I can play games online without fuss.
This is what sdfjkl is intending I think. Have the TVs/Whatever on the other side so they can't scan your network shares to get the information to send back the HQ.
I would be much more effective, straightforward and ultimately more useful though, to firewall the TVs from the internet outbound so they can collect data all they like and never send it home.
Both actually. They might need access to your internal network to access your file shares and whatnot, but you'll want to make sure they can access only the parts you want them to, and nothing else, so they can't for example log onto your unsecured printer and collect a list of most recent print jobs, including filenames.
And they might need to access the internet to download firmware updates and stream video, but you don't want them to "LG phone home" and report your midget porn viewing habits, so you'll block that.
Of course all that requires quite a bit of knowledge, time and equipment to set up and is therefore quite unrealistic, so you're better off just hooking up your laptop via HDMI and putting the damn TV into monitor mode, "smart" be damned.
I've been looking into this possibility myself, as we're currently upgrading our home entertainment systems and I was unpleasantly surprised by the lack of alternatives to "smart" TVs.
Unfortunately, typical home or SOHO Internet and wireless set-ups tend not to support something like shoving all your AV equipment on a separate VLAN when it hits a wireless router. Ideally, you'd probably want either direct access from that router to the Internet, isolated from your main network, or if you've got a slightly more advanced set-up, the ability to set up a static route that will only allow traffic from the AV part of your network to your Internet router, again fully isolated from your main network. Sadly, playing with VLANs tends to need a step up to a more serious level of networking equipment and in particular routing hardware, and the price for that is prohibitive at present.
It would certainly be interesting to see some advances in basic routing coming down into the home/SOHO markets, though, and potentially developments of consumer-friendly hardware firewalls as well. As homes become increasingly networked and automated, I suspect there is going to be a growing market for dealing with these kinds of security issues but with minimal set-up and as few different items of networking equipment as possible.
OpenWRT (and dd-wrt, and I'm sure most other wrt variations) let you set up another "virtual" HotSpot. If your AV equipment can do wireless, that's an option.
Also, I just bought my mom a TP-Link device capable of running openWRT for $25 (don't recall the model). If you care about privacy, it's relatively cheap in enabling hardware - it's your time that is going to be expensive.
I'd rather pursue legal mechanisms than technical ones in this case.
They aren't mutually exclusive. In particular, the very fact that a manufacturer tried to do something covertly as part of another system the customer authorised would potentially make their actions a criminal offence where I am, as it clearly becomes unauthorised access and not merely a privacy or data protection issue mostly likely dealt with through regulation or a civil court.
I can't help thinking that the world would be a better place, and one with a lot fewer of these shady behaviours, if the individuals who were knowingly and deliberately arranging them at each company were personally on the hook for that criminal conduct, and not able to just turn a blind eye and rationalise the abuse away because their employer's lawyers could handle any consequences.
