Why Your Car Thinks You Let Go of the Wheel

From the video's description

Lane assist on a straight road, hands on the wheel, and the car still asks you to hold it. Many cars can't feel your hands at all.
Behind the steering wheel there is a thin steel torsion bar that twists a tiny bit when you steer; a sensor measures that twist.
On a straight road you hardly steer, the bar barely twists, and the car decides your hands are gone. A small nudge fixes it.

The X-ray is a simplified drawing: the twist is shown much larger than it really is, and some cars put this sensor down at the steering rack instead of behind the wheel. Newer cars may also sense hands with a touch-sensitive rim or a driver camera.

Sources: Kia owner's manuals (Lane Following Assist, hands-off warning); Tesla owner's manual (Autosteer: "slight resistance as the steering wheel turns"); electric power steering torque sensor descriptions (torsion bar between input and output shaft).

3D models (CC BY 4.0): "2023 bmw 3 series" (shown without badges) and "Mercedes Vito Utility Car" by solid3ddd · "Volkswagen Golf 8. GTI (A8)" by GT Cars:
Hyperspeed · "2016 Volkswagen Polo" and "Ford Focus Sedan" by BHP3D · "James Scania R440" by zairiq-123 · "Semi Trailer" by NoblecatSoft · trees by Jagobo and lolipop_1707 · "Wind Turbine" by Sket_h · "Power Transmission Tower" by gisexpert · "Residences of Rothenburg ob der Tauber" by Shotkey · "Rural Brick House with Barn and Chicken Coop" by Vitalii.Sandula · "Electrical Steering Column - Pro HD" by MAD CAD LTD · "Cypress tree" by ElectroNick · "Umbrella Pine" by rhcreations.
Poly Haven (CC0). Sounds: blaukreuz, kyles (CC0, Freesound). Music: the channel's own.
The cars are shown without badges. BMW, Volkswagen, Ford, Mercedes-Benz and Scania (in the model titles) are trademarks of their owners; this video is not affiliated with or endorsed by any of them.