Where can an electronic toll transponder NOT be placed?

An electronic toll transponder is designed for optimal performance when placed in specific locations on a vehicle. Placing it in a helmet is not suitable because helmets are not intended to facilitate the functioning of the transponder. The device relies on its placement on the vehicle to effectively communicate with tolling systems, which are often positioned above the road or at toll booths. Proper placement is crucial for ensuring that the transponder can send and receive signals clearly.

In contrast, placing the transponder on the windshield, in a tank bag, or even in a pocket has varying degrees of success based on vehicle design and the transponder's frequency of operation. However, these placements can still allow the device to function properly, as they do not obstruct the signals. A helmet, however, is designed solely for safety and protection and does not provide the necessary environment for the transponder to operate effectively, which establishes why this option is the correct choice in relation to the question.