Our new E-ZPass instructed us to store the transponder in the package it arrived in when not in use to help prevent electronic snooping. Of course, I had already torn open the bag and it was pretty much useless at that point. So I hopped over to Amazon for a solution and found a pair of Faraday Bags for $12. Each has two pouches with the one in the back being the signal blocker. You can also store your car's key fob, contactless credit cards, and smartphones to protect them.