Well, my wife and I have been on a months-long experiment. We have HomePod minis, Macs and iPhones/iPads in the house. They are able to access the internet without restriction (other than using my own DNS resolver for ad/malware blocking purposes.
Our TVs (2020-era Vizio and 2018-era Samsung) are on a separate VLAN for home automation control, and are otherwise blocked from the internet¹. Additionally, they have the various "content intelligence" features disabled...just in case.
We also have a few Nest devices (the 1st gen wired Hello doorbell cam, The Nest/Yale deadbolt, a 2nd gen thermostat, and some Nest Protects) that are normally similarly segmented, though the Hello is allowed to communicate to the necessary domains for video streaming and PubSub notifications.
On August 1, while on a neighborhood walk without any electronic devices, we formulated the plan: every day, we'd find a reason to discuss mulch² in the presence of various devices in our home. What color of mulch we think would look best around various trees. The virtues of recycled rubber as a mulch substitute. The drainage issues it causes. And so on.
We committed to never searching for mulch online (to hide from the ever-present surveillance online), never discussing it with anyone (to avoid social network effects), never buying it (no data broker can hoover up mulch purchases), not dwelling on any social media post about mulch (analytics, man, it's crazy what that bit of metadata can do)...not even hanging around the garden department of local stores (gotta avoid bluetooth/BLE/wifi tracking).
But I DID disable the DNS blocklists (much to our browsing frustration). And while the smart home stuff remained on its own VLAN, I allowed it otherwise unfettered access to the internet during the month of August.
Since the experiment began, we've seen the net sum of zero (0) targeted ads about mulch. No banners, no interstitial social media posts, no phone calls, no flyers in the mailbox. Nothing.
I really don't believe that our devices are eavesdropping on us, but in the interest of science, the experiment continues for another month.³
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1) Yes, I recognize that Sidewalk/ethernet-over-HDMI/hard-coded DNS/etc is a purported "thing", but I don't believe it's likely. I'm controlling for this during the month of September by re-enabling the filtering mentioned at the start; if our TVs are committed to exfiltrating surveillance data.
2) We've not really been discussing mulch. I'm using that as a proxy here, because all of the internet is a series of tubes that lead to advertising networks. But we did choose a unique topic of conversation that would be relevant to our demographics, geographical location, and season, and meaningful to advertisers.
3) On September 1, I re-enabled all the blocklists and VLAN network filters/blackholes. But we continue to discuss, er, mulch. Like I said, if our stuff really really wants to phone the mothership to have Big Mulch pay us a visit, there are supposed to be ways for them to do that. Right?
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EDIT: The topic we chose is also something that's not typically discussed in our social network, nor our kids' social networks. I will say that it's related to a profitable market, and we're in the target demographic, but we did our best to identify a market that we didn't have in common with our social groups.