[kabdib]

You can always ask someone for their badge (either to see it, to verify they work there, or to scan it to ensure it's valid). I'd feel lots more uncomfortable asking someone for their phone.

I've challenged plenty of people trying to tailgate (either on me, or someone ahead of me). I was not shy about calling people on the fact they weren't displaying a badge; we had leaks where I was working, and it wasn't much fun.

Most people took it well. Of the ones who didn't, all but one were non-employees trying to sneak in.