Autonomous vehicles must communicate their autonomous driving state to this sensor.

See also 2027 Official Rules Chapter IV Article 412: Communication of Autonomous State and 413: telemetry

Two terminals (“C” and “1”) of the switch box must be connected to a potential-free contact (e.g., relay output). This contact must be closed when the vehicle is driven autonomously, and it must be open when driven manually. No voltage or pull-up resistor should be connected to the switch box. If the resistance is below 1kOhm the state is recognised as autonomous. If the resistance is above 100kOhm the state is recognised as manually driven. If the resistance is between 1kOhm and 100kOhm the state is not defined.