protective circuits is run out through the switch hole (fig. 8-20). There should be no more than 1/4-inch (0.6 cm) space for windows and 1/8-inch (0.3 cm) for doors between the two sections of the detector.
4. Be certain there is enough space between the window and its frame (or door and its frame) when each is closed; that is, there must be enough space (usually equaling 1/16 inch or 0.16 cm) for the protrusion of both sections when they meet.
5. A switch and magnet are installed preferably in the top of the window and underside of the upper window casing, where they will be least noticeable (fig. 8-21). If the window frame is not thick enough to accept the magnetic section of the detector, the detector can be mounted in the side frame.
A self-adhesive foil block (terminator) on the door is connected to a similar unit on the doorframe by a short length of flexible cord to allow for door movement (fig. 8-22). The foil is connected in the positive conductor of the protective circuit and is adhered to the glass parallel to and about 3 inches (7.6 m) from the edge of the glass, using recommended varnish. Breaking the glass breaks the foil and opens the circuit. A double circuit of foil may be taken from the foil block to provide more coverage. Coiled, retractable cords are available for use between foil blocks to allow for sliding-door travel.
Where a window does not open, a single run of foil is connected to a foil block on the glass, frame, or wall (fig. 8-23). When the foil crosses over a frame member, a piece of plastic electrical tape should be used to provide an insulated crossover surface for the foil.
A glass door with a glass transom may be protected by a combination of magnetic contacts and foil (fig. 8- 24).
The recessed plunger detector shown in figure 8- 25 is mounted so that the door or window will contact the plunger at the tip and push the plunger straight in. Therefore, the area of the window or door that depresses the plunger should have no slots, cutouts, or step-downs into which the plunger might slip. The area also should be hard and free of rubber or vinyl that might be weakened by the plunger and consequently allow the plunger to open. For protecting doors, plunger type of detectors should be mounted only in the doorframe on the hinge side of the door.
In cases where it is difficult to protect a window or door by mounting any of the direct type of detectors, the area directly inside the door or window can be protected with interior "space" detectors, such as a floor-mat detec- tor (fig. 8-26) or an ultrasonic motion detector (fig. 8-27).
Floor-mat detectors are easily concealed under rugs at doors, windows, top or bottom of stairways, or any other area onto which an intruder is likely to step. Light pressure on the mat triggers the alarm.
There are also rolls of super-thin floor matting that can be cut to any desired length. These rolls can be used on stair treads and in areas near sliding glass doors or other larger glass areas, entrance foyers, and so forth. In households with unrestricted pets, these mats are almost useless since the pets roam around the home and are certain to step on one of the mats and trigger the alarm.
Figure 8-20. - Recessed magnetic contacts in door. 8-13Continue Reading