Smart TV makers like LG are sharing viewer data with ad partners that track people from a drug ad all the way to the pharmacy — bad news for anyone who values privacy, good news for advertisers and drug companies.

• By accepting the TV's terms, you agree to send your data to the manufacturer or its ad partners, who match it against their own databases.
• One of LG's ad partners openly focuses on pharmaceuticals and can follow an ad past the click to see whether you actually filled a prescription.
• The TV sees every other device on your home Wi-Fi, so the same ad can be pushed to your phone, tablet, and laptop.
• Once a prescription is filled, the ads for that drug stop and a pitch for a different one begins.
• The same tracking reaches into other connected devices, like a smart water heater that can tell when you need to buy more salt.

Outlook: Expect more scrutiny of smart TV data practices as these disclosures spread, with pressure building for tighter limits on cross-device ad tracking.