Abstract: A hardware assembly providing a motion-activated vent stop for a vent window assembly. The hardware assembly can detect excessive forces acting on the vent and quickly arrest any unintended or induced movement of the vent while enabling the regular function of the vent window under normal operating conditions. When an opening force acting on the vent exceeds a predetermined value, the resulting torque causes a shoe to pivot and engage a stepped profile of a guide slot of a track along which the shoe moves. Once engaged, the shoe cannot move along the track and continued movement of the vent is halted. The shoe includes a biasing member that engages the guide slot and produces a counter-torque that tends to bias the shoe generally vertically in the guide slot and enable the shoe to travel freely under normal operating conditions.