WALTHAM, Mass.— An alcohol-detection prototype that uses automatic sensors to gauge a driver’s fitness to be on the road has been demonstrated for federal transportation officials at a Massachusetts lab.

U.S. Transportation Secretary Ray LaHood and the head of the National Highway Traffic Safety Administration were in Waltham today to see the devices, designed to detect instantly if a driver is drunk and prevent a vehicle from starting.

A woman demonstrating the prototype drank two cocktails over 30 minutes, then showed how breath and touch sensors detected her blood-alcohol level.

Developers say the technology would be less intrusive than current alcohol ignition interlock systems that force drivers to blow into a breath-testing device.

Officials say the prototype is at least eight years from commercial use.

Critics question the cost and reliability.