The vehicle would "passively monitor the performance of a motor vehicle to accurately identify whether that driver may be impaired." And if a blood alcohol level above the limit were detected, the system would prevent operation of the vehicle.
A piece of legislation that was quietly included in the infrastructure bill signed by Biden would give the U.S. government access to a 'kill switch' linked to law enforcement in all new vehicles from 2026.

Under a section in the bill that talks about 'impaired driving technology', the new system would "passively monitor the performance of a motor vehicle to accurately identify whether that driver may be impaired."

If a blood alcohol level above the limit is detected, the system would "prevent or limit motor vehicle operation."

In other words, a kill switch.