That movie was spot-on about so many privacy and surveillance issues we have today (almost 20 years ago...). However Faraday cages were already a pretty known trick, this guy "just" innovated with the material used.
I've watched it 20 years ago so I don't remember seeing such scene. I do remember Gene Hackman explaining about cages when his hideout is shown though.
It's in the scene in the hotel lift - Hackman gets Smith to remove various things, and stuffs the trackers in a foil crisp (aka chip) packet, and the techs lose tracking on them.
