How to tell if light switch box is grounded

I'm attempting to install a smart light switch in an existing light switch box. There's isn't a ground wire I can see, nor does my voltage detector light up when I touch one end to hot and the other to the box. My outlets are all grounded, so could it be that my light switch box is not? This condo was built in 2004 in the Chicago area, so I imagine a ground of some kind must exist.