Fence alarm

Claim 1

An alarm for detecting the surmounting of a fence or other vertical barrier, said alarm comprising plural pulse-emitting switches strategically located in supported relation along said fence so as to cause the transmission of an electrical pulse in response to a vibratory movement of said fence, a stepping switch having circumferentially spaced plural contacts including a starting contact and successively encountered vibration-detecting contacts electrically connected to be operated by said transmitted pulses so as to be urged through movement from said starting contact into contact with said successively encountered vibration-detecting contacts, said stepping switch also having an electrically operated reset coil for being returned to said starting contact from a position at any one successively encountered vibration-detecting contact in response to an electrical pulse transmitted to said reset coil, a timer electrically connected to pulse said reset coil to cause the positioning of said stepping switch at said starting contact at each conclusion of a successive timing interval of operation of said timer, an alarm electrically connected to be selectively operated by said transmitted pulses, and a rotary switch having cooperating contacts in substantial relation therewith as said successively encountered contacts are related to said stepping switch, said rotary switch being electrically connected in circuit-completing interposed position between said stepping switch and said alarm so that said circuit therebetween is completed only when said stepping switch and said rotary switch are each at cooperating corresponding circuit-completing contacts, whereby an imposed condition for operation of said alarm is the completion of said circuit as provided by the selection of a rotary switch contact within said timing interval of said timer, and thus a condition contributing to minimal false alarms.