Interlock is a device that is attached to a vehicle so that the vehicle cannot be started without the driver submitting a breath sample that has no alcohol. The device also requires randomly timed tests throughout a journey. It is essentially an RBT unit that controls whether or not you can operate your vehicle.
Until last year these devices were used voluntarily by corporations who wanted to ensure safety, or by people who had been caught drink driving and wanted to make an application for a quicker return to driving. These devices are expensive, typically over $2,000, and so cost has been a barrier to more widespread community use of the program. They are now mandatory for certain serious drinking offences, or for certain repeat drinking offences.