Number one choice for gas powered rigs. The Stay-IN-Play DUO supplemental-braking system is installed so there is no set up required for towing your vehicle. To get ready to tow you simply turn it on; that€™s all. Turn it on... and tow. The DUO energizes the towed vehicles power brakes so it is gentle and consistent. Air Force One is the only air brake system that energizes the towed vehicle's power brakes through a patent-pending process that does not require an electronic vacuum pump. In fact, Air Force One has no moving parts to wear out at all. Air Force One is also the industry's first and only supplemental brake system that protects the coach with a patent-pending breakaway system that seals the coach's air supply in the event of a separation of the coach and the towed vehicle. SMI braking systems are truely unique. Both systems utilize the towed vehicle's power brakes, allowing for soft, effective braking. With the use of Dual-Signal Activation, the Stay-in-Play DUO braking system CANNOT activate when you don't want it to, even down a grade; and with the Air Force One, you get true mirrored braking. The movement of the coach's brake pedal is identically reproduced in the towed vehicle; progressive and directly proportionate braking effort. Best of all, it's all automatic! Both models include coach notification, so you always know exactly how and when your brake is performing.