I rented out Tesla S recently with my friends to try out - doing SF to Monterey and back.

When I was driving, holding hands on a wheel all the time, the car kept giving me notices to put hands back on the wheel. After the third time it refused to reengage the autopilot.

I guess my grip wasn’t strong enough for it to notice.

On the way back my friend did a few short stretches letting go of the wheel completely (still fully alert and hands an inch away), and the car failed to notice.