Safety Lock Model # 091-148-12 The Model 091-148, Safety Lock, is a controller which permits unattended engine operation with the ignition key removed, but prevents unauthorized use of the vehicle. Safety Lock 3 Model # 091-155 The Model 091-155, Safety Lock 3, is a controller which permits unattended engine operation with the ignition key removed, but prevents unauthorized use of the vehicle. For vehicles that require 3 independent relays for the vehicle ignition. Safety Lock 4 Model # 091-160 The Model 091-160, Safety Lock 4, is a controller which permits unattended engine operation with the ignition key removed, but prevents unauthorized use of the vehicle. For vehicles that require 4 independent relays for the vehicle ignition. Safety Lock D Model # 091-174 The Model 091-174, Safety Lock D, is a controller which permits unattended engine operation with the ignition key removed. Designed for Chrysler and Jeep Vehicles that are designed with anti-theft components to prevent running the engine without an ignition switch key.