When is it Science Fiction

I have a friend who argue that Slaughterhouse-5 is not science fiction, and according to him Kurt Vonnegut felt the same way. I think he was wrong. The story is about someone who got unstuck in time, that is either science fiction or fantasy take your pick, but the line isn't always so clear.
Is a detective show which uses technology that doesn't actually exist to show how they solve a crime in a easier way science fiction? Probably not, the technology doesn't effect the plot it just makes things easier. What about A show like Life on Mars, which, from the previews, appears to be a 70 cop drama except that a modern day investigator is stuck in that time. Again, I haven't watched it, but I get the impression that while he uses modern technology to solve crimes the time aspect of it is not all that important.
Does something rise about fantasy or science fiction when it starts to be about characters? I don't think so, i think that the best science fiction is about characters we care about. It is science fiction because there is a basic scientific idea at the center, which doesn't exist and couldn't be removed from the story without changing it completely. From this idea, Slaughterhouse-5 is science fiction, and CSI is not. Which is good for me, i get to claim the masterpiece and allow the franchise to remain safely in the hands of the mainstream.