THE ELECTRIC BURGLAR-ALARM. 



63 



The cost of applying the burglar-alarm to any house will vary 

 in each case. It depends upon the size of the annunciator required 

 and the number of openings to be protected. The prices charged by 

 the different American manufacturers differ very little. Annuncia- 

 tors range in price from thirty dollars with four indications to one 

 hundred dollars with twenty. The annunciator used should have as 

 many indications as there are rooms protected. The cost of circuit- 

 closers, including the placing in position and laying the wire, is three 

 dollars a window when both sashes are connected. The same devices 

 for doors vary from one and a half to two and a half dollars. In 

 ordinary city houses it is only necessary to connect the windows and 

 doors, front and back, of the first two stories and the opening in 

 the roof. The entire cost will not generally exceed one hundred 

 dollars. In the country the cost would of course be somewhat greater, 

 in the average house probably between a hundred and fifty and two 

 hundred dollars. The apparatus once in, the only expense is the main- 

 tenance of the battery. This will generally be very small, probably 

 not more than a dollar a year. Considering the security gained, the 

 outlay required is not excessive, and builders find that it is fully 

 made up to them in increased rents. It is not improbable that the 

 apparatus will eventually be considered as necessary to the complete 

 equipment of a house as now are water- and gas-pipes. 



Intimately connected with the burglar-alarm system, though having 

 a different object, is an automatic fire-alarm, somewhat extensively in- 

 troduced during recent years. The system consists in placing in the 

 ceiling of a room a number of mercury bulbs, which close an electric 

 circuit when the temperature rises above a certain point and set off an 

 alarm. One form of the bulb or thermostat is shown in Fig. 4. The 

 wire from the lower end is in permanent contact with 

 the mercury, but that in the upper end comes in 

 contact with it only when a given temperature is 

 reached. The bulbs are usually manufactured to 

 make this contact at a temperature of 120 Fahr. 

 The thermostat is set in a bell-shaped shield of sheet- 

 metal, only the rim of which, when in the ceiling, 

 is exposed. They are placed about twenty feet 

 apart in large rooms, a couple being sufficient for 

 those of ordinary size. This alarm, like that for 

 burglars, may be complete in a building, or may give 

 its signal at a central office. In some of the larger 

 cities this latter plan has been carried into practice. 

 Each building is provided with an annunciator placed 

 on the front, where it can be readily inspected. The 

 signal given at the office indicates the building, and 

 the annunciator on the face of the building gives the room in which 

 the fire is located. 



Fig. 4. Tnnp.MOSTAT. 



