I think the newest transponders are actually the transparent RFID stickers that are smaller than even the "FastTrak Flex" batteryless switchable transponders.

I think the newest transponders are actually the transparent RFID stickers that are smaller than even the "FastTrak Flex" batteryless switchable transponders. Note that the different FastTrak operators in California have DRASTICALLY different fee structures. Some have monthly fees, some don't. Some charge for switchable transponders, some give them for free, some require a deposit, some only need your license plate # to charge you, etc.