Window security screens are intended to make things difficult for criminals who choose to break into your house. So difficult that the end up moving on to an easier target.
Most break-ins are crimes of opportunity. Criminals find an open door or a half open open window. Or a screen thats easily removed from the outside.
They gain access to the house and grab what they can and run. If its the least bit difficult to get in, if it means they have to take time and make lots of noise breaking glass, its unlikely the criminal will go through with the break in. They dont want to attract attention.
Many methods can be used to make screens the first line of defence in preventing break-ins. One method is to use steel screen material thats tough to cut through. You can use galvanized steel and stainless screening which is difficult to cut through.
Home security window screens can also be screwed into place on the inside all around the frame making it very difficult for the criminal to rip them out.
Security window screens can also become part of the alarm system. There is fiberglass screen cloth made with conductive wires as part of the weave. These screens can be wired into the house alarm system so that if they are ever cut or removed the alarm goes off.
This stops the criminal before they even get to trying to force the window or door behind the screen, giving police time to respond to the attempted break-in.