We love this product because it serves two important purposes: 1) prevents your battery from draining while your car sits idle, and 2) foolproof theft prevention. Simply connect this cable to your positive or negative battery terminal, then when you leave your car just remove the green knob and the power is disconnected. Thieves will not be able to start your car. Don’t worry – it allows just enough power to get through so that your clock and radio settings will not be lost. Ingenious, no?