A safety stop device for limiting the movement of a window or sliding door that is fitted with a glass pane. The safety stop has a housing with a top plate. The top plate is flat. Support walls extend from the top plate and terminate in a common plane. A protected area is defined between the support walls and under the top plate. A suction cup is disposed within the protected area. A suction control assembly is coupled to the top plate. The suction control assembly selectively controls air pressure within the suction cup when the suction cup is engaged with the glass pane.