Leave your windows down, then nobody will break in.

Any "film" won't be effective to keep someone out of your car. They're STILL going to break the window. You'll STILL have to replace it. And they'll STILL get in your car. Except they'll be pissed because it took more work than expected.

On a side note. Coworker locked her keys in her car.

She broke a window to get in, rather than calling for a locksmith.