BURGLAR ALARM.

Auckland Star, Volume LXII, Issue 6, 8 January 1931, Page 5

BURGLAR ALARM.

ULTRA-VIOLET LIGHT RAYS

WONDERFUL DEMONSTRATION. A recent cable from London stated | that at the international exhibition of Persian art a most striking display is contained in a showcase guarded _by radio visor light with a sensitive bridge and that any interruption of the ray releases a switch and illuminates a warning signal in the main entrance and turnstiles of the exhibition, closing all doors. Interesting comment on this now development is made in the last issue to reach New Zealand of the English illustrated paper, "Modern Wireless." A demonstration was recently given in the United States by the Westinghouse Lamp Company to show how a beam of ultra-violet light can be used for the protection of valuables, or as a burglar alarm. It is science's latest assistance to the enforcement of law and order. To show his confidence in the new discovery, the demonstrator placed a 50dollar bill in the safe used in this demonstration, turned the combination off, closed the door and informed the audience, which included representatives of the Police Department of the City ot New York, that anyone who could get away 'with the money without sounding the alarm was welcome to it. In demonstrating the invisible light as a burglar alarm,.a sft safe was placed in the centre of the stage facing the audience. Two ordinary tables abou waist-high were placed 12ft apart. On one was the light source and on' the other the light-sensitive apparatus. When the ray was interrupted by anyone attempting to open the safe the photo-electric cell was affected, causing the anode tube to glow. When ..his occurred it energised the bell i elay. Other devices have been developed m which the photo-electric cell is used. Everyone entering the room was automatically counted as he crossed the beam of light, which was thrown across the floor. , The shadow of a passing body caused i the "electric eye" to communicate with a. counting machine.