snooping through open windows
If I'm in my house playing music and the window is open, is it unreasonable for me to assume that someone passing won't note the location, and what was playing at the time? Or that they would then use that to create a service which tells other people if they can hear particular music then they're probably close to my house? How about if they used it to make a guess at my music tastes, and sold that information to a direct marketing company? What if they overheard an argument, and the next day I get a mail drop from a counselling service?
The problem is not that they eavesdrop on what's going on, it's the way they will use what they heard as they went past.