Futaba gives added peace-of-mind for drivers. The FSU-2 Micro Fail Safe Unit prevents runaways by automatically throttling back the servo to a pre-programmed setting if the event of interference or low battery voltage. Can be adapted to work with 4.8V (4-cell) or 6.0V (5-cell) voltages. Offers the ease of one-button programming and an LED for status. Unit simply plugs in for quick installation, and works with any scale of R/C car or truck.