A new study finds ignition interlocks, devices that prevent a person from starting a car if their blood alcohol level is too high, prevents deadly accidents.

Ignition interlocks are associated with a 7 percent decrease in the rate of fatal crashes involving at least one drunk driver, researchers report in the American Journal of Preventive Medicine. Cars with the device will not start if the driver’s blood alcohol level exceeds a preset limit, HealthDay reports.

While all states have some type of ignition interlock law, only half require everyone convicted of a DUI to use the device, the researchers noted. Some states require them only for repeat offenders, or for those caught driving with very high blood alcohol levels.