Scan with your phone's camera and open the link. On the phone, tap Use this phone as a sensor and enter:

Waiting for your phone.

Works on any network: both devices just need internet. The link goes direct when it can and through a relay when it cannot. Lowest latency: the car on this phone’s Wi-Fi hotspot.

The phone can send the same data as high tones, which this screen hears through its microphone. No code needed. The sound is decoded here and never recorded or sent anywhere.