Abstract: A sonic alarm device is provided for signalling the opening of a door which is hingedly mounted adjacent the edge on a door frame for swinging movement about an upright hinge axis into and out of a closed position. The door alarm is mounted in the interior of the door. The door alarm comprises a housing for the alarm, an isolator inside of the housing, wherein the isolator supports a sonically activated device. A spring holder is mounted within the isolator, and spring is mounted on the spring holder in a position horizontal to the door. When the door is in a closed position, the spring is pushed back into the interior of the housing; the spring is designed to be released when the door is opened. A hammer actuator is contacted by the spring when the door is opened, and a hammer is struck by the hammer actuator when the door is opened. The hammer then contacts a sonically actuated device to cause the device to produce an audible sound.

Abstract: Digital control apparatus for automatically slewing i.e. orienting a directive antenna to a quasi-stationary transponder such as a synchronous satellite in orbit above the earth wherein appropriate drive signals for the elevation and/or azimuth axes are provided in response to the received signal from the transponder until the peak or substantially maximum signal strength is sensed. Operationally, digital logic circuitry utilizes the characteristics of the antenna beam pattern to detect the approach toward zero slope near the peak of the pattern to slew the antenna to the peak signal.