You must keep your hands on the steering wheel at all times.
When the system is active and detects no steering activity for a period of time, the system alerts you to put your hands on the steering wheel. If you do not react to the warnings the system cancels and slows your vehicle down to idle speeds while maintaining steering control.See  Lane Centering Automatic Cancellation . 
The system also alerts you if your vehicle crosses lane markings without detected steering activity.
Note:   The system could detect a light grip or touch on the steering wheel as hands-off driving.