If you've bought a new car in the past half-dozen years, there's a good chance it has a "black box" that activates if you brake suddenly, swerve off the road or hit something hard enough to make the airbags deploy.

The black box is formally known as an event data recorder (EDR), and today it's in 96 percent of new cars sold in the United States, according to industry estimates.

Event data recorders aren't actually black boxes but tiny microcomputer chip sets. In most vehicles, they're part of the airbag control module, and originally were included to ensure airbags deployed when they were supposed to.

Over the years, as electronics got cheaper, smaller and smarter, event data recorders became capable of doing more than simply monitoring airbags. Automakers realized the devices could be used to provide information about the seriousness of an accident, and if a car was being operated properly when a crash occurred. Based on a separate NHTSA regulation passed in 2012, if a vehicle today does have an event data recorder, it must track 15 specific data points, including speed, steering, braking, acceleration, seatbelt use, and, in the event of a crash, force of impact and whether airbags deployed.

Most event data recorders are programmed to record data in a continuous loop, writing over information again and again until a vehicle is in a front-end collision or other crash. When an accident occurs, the device automatically saves up to 5 seconds of data from immediately before, during and after an incident.