Adam Breeden/ZDNETFollow ZDNET: Add us as a preferred source on Google.ZDNET's key takeawaysSmart TVs track viewing habits with ACR tech.Collected data fuels billions in targeted ads.Turning off ACR protects privacy but takes effort.Did you know that whenever you turn on your smart TV, you invite an unseen guest to watch it with you?These days, most mainstream TVs use automatic content recognition (ACR), a type of ad-tracking technology that collects data on everything you watch and sends it to a central ...