What are those orange or white balls that hang on power-lines above random roads?

Honestly, the person to answer this will be the first person I have ever known to actually know what the hell those things are. I see them a lot in Pennsylvania. The balls vary in color, but they are usually orange and sometimes white. They can be as low as fifteen feet or so above the road, and a lot of people have guessed that they have something to do with airplanes, but no airplane would ever be that low, so I really think that’s wrong. They are usually connected about 5 or 6 of them on a line of some sort. It looks like a power line. Then, sometimes they can be from one hill, across a small valley, to the top of another. What the hell are they!