Attach a personal transponder to the windshield of a rental car via a suction cup holder, leave it on the dash, or hold it up with one hand against the windshield whilst driving (admittedly, the last is unsafe and possibly a moving violation in some jurisdictions). Hertz transponders are encased in a shielded box that is mounted on the windshield; the transponder slides in and out of the box. Ensure the Hertz transponder is completely slid into the shielded box to ensure it isn't read by an electronic toll reader.