Many motorists don't know it, but it's likely that every time they get behind the wheel, there's a snitch along for the ride.

In the next few days, the National Highway Traffic Safety Administration is expected to propose long-delayed regulations requiring auto manufacturers to include event data recorders—better known as "black boxes"—in all new cars and light trucks. But the agency is behind the curve. Automakers have been quietly tucking the devices, which automatically record the actions of drivers and the responses of their vehicles in a continuous information loop, into most new cars for years.