Jamie De Lisle's Buick had been warning her for days, first with a flashing yellow light, then a flashing red light. But the 31-year-old mother of two from Collinsville, Ill., was too busy to heed the distress signals. It was only when Mrs. De Lisle began hearing an incessant beeping that she took notice: If she didn't make her car payment that day, the vehicle wouldn't start the next day.

The repo man has found a new hiding place -- inside your car. Increasingly, used-car dealers are installing remote disabling devices that...