"If you choose to enable a feature called "More Ways to Watch" on your Roku TV, then in addition to the viewing information and other information that Roku collects from your Roku TV as described elsewhere in this policy, Roku may also collect viewing information using ACR. If "More Ways to Watch" is enabled, Roku uses ACR to help Roku identify the networks, channels, and programs you watch and when you watch them via your Roku TV's antenna or devices connected to your Roku TV's input ports, including over-the-air broadcasts and cable set-top boxes. Based on this information, we may recommend personalized content, serve personalized ads to you and measure viewership of ads and programming.
We may supplement this viewing history with other demographic data we learn about you. We may also share viewing data derived from ACR with third parties such as measurement providers in an aggregate manner or in ways that do not personally identify you directly."
TechCrunch reports that this data collection only happens during use, and since ACR isn't a microphone, it won't be listening when your set is powered off. And again, the only way any of this works is if you opt in. If you'd rather it not happen, it's as simple as not agreeing to it when prompted. Vizio, on the other hand, recently came under fire for making its data collection opt-out, versus opt-in.