Key fob faraday pouch

[Atlas]

It's more than just the fob talking to the truck. The truck has a receiver that's listening for the fob as well as a computer/infotainment that may be searching for, or sending/receiving signal and location to OnStar (even if you don't pay for a plan) and or checking for software updates. The truck also keeps various other modules alive with the key off.

 

It's a good idea to trickle-charge any modern vehicle that may sit for extended periods. Putting the fob in a faraday bag won't prevent the other electrical drain.