Use of ignition interlock devices is a growing trend across the nation to control the number of DWI/DUI arrests in the country. A recent study indicates that the number of the devices that have been installed has more than doubled across the country in the last five years. The national study says that roughly 249,000 cars across the country now have ignition interlock devices installed. That number is a significant increase that the roughly 101,000 cars equipped with the devices in 2006.