I have one on my D. It is attached to the battery behind the passenger's seat and works by pressing a button. I use it to "cut" the battery if I haven't used the car in several days. I find it works great for my use, i.e., to preserve the battery. But if you are looking to use it as a anti-theft device, you might want to position a switch in a somewhat more convenient location, as in that case you would probably be wanting to use it several times a day. I believe battery switches can be obtained from Sears, Pep Boys, or other auto parts stores.