Abstract: A security device for the prevention of theft is described. It comprises an alarm, a motion detector which provides a signal, effective through an electrical circuit for actuation of the alarm. The motion detector includes a tubular cylinder, a sphere and a tether which are conductive and connected in series across an electrical potential. Movement of the detector, from any initial orientation and in any direction results in an increase in contact resistance between the sphere and cylinder and generates a motion signal. After actuation of an arming switch, a motion signal energizes the alarm. Once armed, a disarming switch must be actuated to prevent or halt energization of the alarm. The device is detachably mounted on a brief case, with the switches on the exterior and connected by conductors to the remaining elements of the device mounted on the interior of the brief case.