Smart TVs are quietly listening in living rooms, and there is little owners can do about it — bad news for anyone who assumed a dark screen meant a dead device.

• Lab testing of LG OLED TVs found the built-in microphone stays on in standby, saving clear audio locally even with the network unplugged.
• That stored audio was later pulled off the TV through security flaws once it reconnected to the internet.
• The TVs also scan the home network and map every other connected device, from speakers to Wi-Fi appliances.
• Former NSA official Thomas Drake says none of this is new — smart TVs were never built with security in mind, and both companies and governments have every incentive to hoover up the data.
• Turning the set off does not stop it; only pulling the plug does, and some models have cameras too.

Outlook: Expect pressure on TV makers over default settings and microphone access, but no quick fix for the millions of sets already in homes.