Can I replace 1 switch of a 3-switch box with a Motion Detector switch
A three way switch is a single pole double throw switch and will not work with a single pole single throw switch like a motion sensor switch. A three way switch has two switch legs and one common lead. You could wire the motion sensor in series with one of the commons of either switch and the light would stay off when no motion was sensed. Once motion was sensed the three way switched would work normally.