Electronic immobilizers work in conjunction with the conventional key; this most often involves a small transponder located in the key that emits a radio signal with an electronic code. Although the EU legislation did not become effective until October 1998, most vehicle manufacturers began installing immobilizers as standard equipment from 1995 onward. In the United Kingdom the Home Office Car Theft Index has been published annually since 1997; it shows a risk of theft for all major car models. Since 1998, separate indexes have been developed on unrecovered vehicles, so as to show changes in the pattern of permanent theft. This means that theft rates are available on all vehicles stolen, on unrecovered stolen vehicles, and on recovered stolen vehicles for those stolen between 1998 and 2001. Data from these 4 years were used in the current study. The study examined the changing age profiles of stolen vehicles. It concluded that although electronic immobilization has had an impact on temporary theft ("joy riding"), there are indications that professional car thieves may have found new methods to overcome electronic immobilizers. 5 figures, 1 table, 9 notes, and 15 references