The break buddy applies brakes every time the towed SLOWS DOWN it is operated by an inertial sensor.
Of course this assumes you install it properly EVERY TIME YOU TOW, which is the biggest reason I don't like this type of system. Too easy to say "oh forget it" on a short trip. And later wish you had not.
Other systems, generally also work every time you apply the motor home brakes, but once installed they are "invisible" when not operating in towed mode. and thus since activating them is a few seconds, less likely to "Oh Forget It".