An ignition interlock device is a device that operates like a breathalyzer that controls your ability to start and operate your vehicle. Typically, there are two components to an ignition interlock device. One is the actual handheld device itself, which you will blow into in order to have your blood alcohol concentration tested. The other is a component that connects to your vehicle and has control over certain functions – like allowing you to start your car, for example. A cable links the two devices, although in some instances they may communicate with each other wirelessly.

The governing authority in your state will calibrate the device itself. They will determine a blood alcohol concentration threshold for the device. When you blow into the ignition interlock, the device will measure your blood alcohol concentration and determine if it is above or below this mandated threshold. If it is above the threshold, then you will be prevented from starting the car. Otherwise, you will be able to operate your car as normal.

In addition to a test that is administered when you start the car, some states mandate that these devices administer random tests while the car is in motion. When it is time for a random test, the device will signal the driver, who will then blow into the device as before. Provided that the driver’s blood alcohol concentration is determined to be below the device’s threshold, the car will continue to operate normally. If, however, the driver is determined to have a blood alcohol concentration that is in excess of the threshold, the car itself will begin to signal loudly, and the driver will have no choice but to pull over and turn the car off in order to stop it from signaling.

Typically, an ignition interlock device is interfaced with an electronic log, which keeps track of tests that the device administers. In almost all cases, the authorities will require the driver of a car equipped with an ignition interlock device to come in periodically to have these logs checked. In some cases, though, this log will be transmitted wirelessly.