Robert N. Staples.

It is commonly supposed that burglar alarms are expensive to install, are complicated in construction, and require a considerable amount of electrical experience to maintain. Nothing could be more erroneous. Anyone who will carefully follow these directions may install alarms, and accomplish absolutely perfect results. Burglar alarms are suited for doors, windows and bulkheads of houses and workshops. and suitable apparatus may also be connected with gates, stairways, doormats and carpets, with wiring so concealed that it cannot be tampered with. By the aid of the following descriptions and diagrams, installations may be successfully made with very few tools.

Fig. 1. Open Circuit D00e Spring

Fig. 2. Closed Circuit Door Spring

Fig. 1 represents a type of open circuit door spring. This device is fitted in the framework of the door jamb, near the upper hinge, by boring a half-inch hole into the jamb. This device is just the reverse of a push button: that is, a push button, when pressed, connects two contact springs and completes the circuit through battery and bell. In the door spring the closed door keeps the button pressed way in, and the contact is only closed when the opening door permits the press knob to come out. In this device a door left open leaves the alarm in continuous circuit, so another device having a wide contact, or make and break device, Fig. 2, is designed to close the circuit through the bell while the door is opening and closing, but the bell does not sound when the door is completely open or closed. Another device to perform this same service is the door trip, Fig. 3, which is installed over the door on the inside, and announces the entrance of any one by ringing a bell when the door passes the trip, but is silent when open or closed.

Window springs, Fig. 4, are set into the window frame by boring or cutting a small hole in the frame itself, and a V-shaped cut made in the sash. When the window is closed the V-shaped part of the

Fig. 3. Door Trip

Fig. 4. Window Spring device fits freely into the niche in the sash and the circuit remains open until the window is moved upward, when the V wedge is forced back into the device and rings a bell the same as any ordinary push button. This device makes one of the best burglar alarms for a store or office having a window out of the range of general observation.

Often times any of these devices may be connected to advantage to an automatic drop, Fig. 5. by which the alarm, once given, will continue ringing until the drop lever is replaced by hand.

It may be said to advantage, right here, that it is best to select an alarm bell that will keep dust proof and in perfect adjustment, and it is advisable to select a large gong, say 3 1/2 or more inches diameter, with sufficient battery supply to bring out all the sound there is in the bell.

Electric burglar alarm matting is constructed along the lines of push buttons; that is, the carpet or matting has push button contacts all along the under surface, and the lightest tread on the matting rings the alarm bell. The matting is sold by the square foot and is used in front of safes, stairways and doors.

Fig. 5. Automatic Drop

Fig. 6. Alarm Trap

Properly adjusted throughout a residence or store it proves a most satisfactory appliance. Fig. 6 illustrates a device which may be placed across a path or hall or

Fig. 7. Alarm Circuits, stairway, and by means of a dark and inconspicuous thread or string the alarm is set off electrically, should the thread be cut or pulled by a trespasser.

Now, as to methods of wiring. It was in the early days of bell wiring desirable that the batteries be placed on a shelf in the cellar or basement out of harm's way. But with the introduction of the dry cell much of this practice was done away with, because dry cells never leak or damage surrounding objects and may be stored on shelves or in any convenient place, at the owner's option. Dry cells are very popular for burglar alarm work and, because of their cheapness and cleanliness, are commended for this service. The best quality of insulated wire will be

Fig. 8. Alarm Matting

Fig. 9. Annunciator found the cheapest, and the gauge No. 18 is most desirable. Tacks should never be placed over two wires. Fig. 7, A, illustrates a circuit comprising one burglar device, battery, wiring and bell. In B is shown one set of batteries operating one alarm bell connected to three burglar devices. In C we have two bells operated in multiple by one device and one set of batteries. Fig. B illustrates two bells and devices, one battery, and both bells ring when either device operates.

Fig. 9a. Four Drop Annunciator Circuit

In connection with burglar alarms, where there are more than two doors or windows equipped it is often the practice to install " annunciators " to register the exact location of the alarm. Fig. 9 shows an annunciator of a reliable type. The names, or numbers, of the doors or windows can be noted on the shutters when desired. The cases are finished in polished hard wood and look well in any part of the house.

Fig.9A shows an annunciator circuit for four devices which may be on doors, windows or matting as desired, a set of batteries, a loud ringing bell and an indicator for each device. Thus, the annunciator signal tells at a glance which signal has operated. By this system quicker action can be taken in time of emergency because the exact location of the trouble is known immediately.