With the surge in the crime rate in general and, particularly in the burglary rate, there has been a proliferation of protective devices, directed mostly toward prevention of illegal entry through doors. Bars and gratings of various types have been placed across windows but, in addition to being unsightly, these constitute a serious danger in that they may prevent rapid escape in the event of fire. Moreover, the cost of such devices, when added to installation costs, makes complete protection of all windows in an apartment or home almost prohibitively expensive. Somewhat the same problem arises with respect to sliding doors whether of the type where a single door slides into a wall or the double type where either of a pair of sliding doors can be moved past the other.
While complete prevention of illegal entry by intruders provides the ultimate in protection, nevertheless, an effective alarm system, which is sufficiently inexpensive so that it can be widely applied, can provide a measure of protection which substantially increases the security of the inhabitants. As is evident, then, an inexpensive but effective device, which is reliable and readily installed, is desired.