Do they make a device that you could scan over a sentence in a book, and it would take notes on that?

I like to take notes on what I read, and it's too hard to drag my computer everywhere that I want to read, and I can't highlight because these are library books. Is there such a thing as an electronic highlighter that when you run it over a sentence, it would put that in memory to be uploaded to the computer? Or is there anything close to this idea at all?