I never thought about it but the E-ZPass technology is actually incredibly basic. Using RFID technology your tag is scanned and validated at every toll booth. The technology is so simple that your tag could even be scanned somewhere other than a toll booth by someone other than E-ZPass. Without any protection your E-ZPass tag becomes a tracking device for someone with a little know how and some outdated technology. Maybe someone like the government.
New York City is actively tracking the tags placed on your window or against your license plate with the goal of monitoring the cities traffic in a project called "Midnight in Motion." The only way to prevent being tracked is by using an RFID-Proof container at all times except the times your actually paying a toll. Not so convenient any more for the privacy conscious.
E=ZPasses Get Read All Over NY