Automobile theft alarm

Claim 1

An alarm for indicating the unauthorized use of a vehicle of the type having a voltage source having first and second terminals at first and second different voltage levels, at least one load device, first switch means and means connecting said load device and said first switch means in series across said voltage source whereby said first switch means is effective when actuated to operatively connect said load device across said voltage source to cause a supply of current to flow through said load device, said alarm comprising, warning means, voltagesenSitive semiconductor switch means in operative circuit arrangement with said warning means and effective when actuated to energize the latter, said semiconductor switch means having a control terminal, and means operatively connected to said control terminal and said voltage source and effective, when said first switch means is unactuated to provide a conductive charging path from said first terminal of said voltage source to said control terminal to charge said control terminal substantially to said first voltage level and when said first switch means is actuated to develop a voltage signal at said control terminal at a level different from said first voltage level in response to the current flow through said load device to actuate said semiconductor switch means, thereby to energize said warning means, and manually actuatable disabling switch means accessible from the outside of said vehicle and operatively connected to said semiconductor switch means and effective when actuated to disable said alarm irrespective of the condition of said first switch means.