Smart TV apps are Web apps. If you are you using .net to develop the web app you might need to check on https://github.com/xamarin/Xamarin.Forms for help on that.
Thanks for the quick reply Ron - I am a bit confused now… AFAIK is a web app not a native app (xamarin is a native app dev. framework … but you also mention in the beginning “smart tv apps are web apps”??) … apart from that, my main question was if one can access from a smart tv app the proximity sensor = is your answer “if one uses xamarin framework, then yes”, or is it accessible anyway, no matter what framework one decides to use?