<sigh>
The tool in question is a radio frequency "spoofer" that is, ironically, a direct offshoot of the same DECT technology that makes your wireless house phone work better.
It's not an "amplifier" (as in it doesn't make a signal stronger), it's a fast processor that sends a set of pre-known signals in a brute force attack and "listens" for a response to find the correct code.
You can basically think of the old "safecrackers" in movies who listen carefully to the tumblers while dialing a safe.
Putting your fob in a foil pouch or faraday cage won't do a thing against this sort of hacking because it doesn't involve the Fob at all (at least not for Chevrolet's design).
There is also a "replay attack" that can listen for a fob, record it, and play it back, but that happens when the fob is actively being used, not when it's just sitting around.
[EDIT: older cars are still more vulnerable to radio hacking since the
Keeloq wireless entry cipher got cracked a few years ago].
Cars are in serious need of TWO factor authentication.