How can my browsing habits be traced when I am at home on my own local network?
Technically how is it done ?
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HTTPS is not designed to keep people from sniffing your browsing habits, and doesn't really protect you from this. Anyone able to sniff network traffic (your ISP, for example) can see https DNS and domain requests just as easily as http-- this allows visibility into what servers/IPs you have requested.
HTTPS only protects the CONTENT of the pages viewed, as well as protecting against man-in-the-middle attacks (modifications of pages on their way to you).
Protecting outsiders from sniffing your browsing habits involves other technologies such as TOR/Onion, or encrypted tunnelling/VPN.
It doesn't matter where you are. Traffic leaves your device and travels over the network to the target. If the traffic is not encrypted (HTTPS, for example), those in that path on the network (the Internet Service Provider, for example) can see and read that traffic.
If you are connecting from a home device to another home device, then those on your home network can see that traffic, but those on the Internet cannot.
As for "browsing habits", that's a different story and that involves "cookies". When you visit a website, they store cookies on your machine that can end up being read by other sites. This is how ads on sites you have never visited before are still targeted to you, because the ad network stored a cookie that is read by other sites using that ad network.