If this is going to be for a house there are two different types of switches, surface mount and recessed.. The surface mount is as its name implies, mounted on the surface of the door/window with wiring exposed. Recessed has the magnet placed in a 3/8" hole drilled into the edge of the door,and the switch in another hole drilled into the door casing, wiring concealed in the wall. Either of these switches should be mounted on the knob side of the door, so that pounding or flexing of the door will set off alarm.
When installing switches the magnet must be placed as close as possible to switch, and in the case of recessed , the alingment must be even...When you get the switches, connect a ohm meter to it and place the magnet near to it to see how much of a gap will open the switch..