Unusual little device chambered for .22-caliber percussion. Consists of approximately 1" rectangular brass block, with a chamber bored into it that accepts a black-powder charge. No provision for a projectile. There is a spring retained arm on top, which works as a hammer. As the device is activated by a door or a window, hammer snaps closed striking a percussion cap that causes the charge to fire, thereby creating an alarm notifying that the perimeter has been breached. Marked "J. P. Wilson/Patented Feb. 8, 1859/Ilion, NY".