Door alarm controlled by operation of door lock

Claim 1

A burglar alarm device comprising: a door lock attachable to a door, said door lock including a cylinder and a rotary axle extending through said cylinder; a switch positioned to be closed by a locking operation of said door lock; a door switch positioned to be closed by an opening operation of said door; a self-latching electric circuit means connected to said switches for maintaining a conducting state caused by a closing operation of said door switch when said first-mentioned switch is closed; an alarm connected to and controlled by said circuit means; and said first-mentioned switch comprising a switch box fixed to the outer surface of said cylinder of said door lock, said switch box having therein a semi-circular recess, a slider slidably movably positioned within said recess in said switch box, said slider having therein a groove, means for moving said slider within said recess in said switch box upon locking and unlocking movement of said door lock, said moving means comprising a projection having a first end fixed to said rotary axle of said door lock and a second end extending into said groove in said slider, said projection extending through said cylinder, a two-part first conductor and a second conductor facing said first conductor, one of said conductors being on the inside of said switch box, and the other of said conductors being on said slider, whereby a locking operation of said door lock causes said second conductor to bridge the two parts of said first conductor, thus closing said first-mentioned switch.