Abstract: Method and apparatus for automatically controlling the opening and closing of a door by: (a) ultrasonically monitoring a predetermined approach area located in front of the door for the entry of an object into the approach area and the movement of the object towards the closed door; (b) ultrasonically monitoring a predetermined opening-door protect area laterally outwardly of the outer end of the closed door, and a predetermined closing-door protect area inwardly of the inner end of the door for the presence of an object in the opening-door and closing-door protect areas; and (c) controlling a drive in response to the above monitoring operations.

Abstract: An intrusion detector and method of operating the detector is disclosed. The detector comprises a means including an antenna for transmitting spaced pulses of radiation energy of a given frequency throughout a region to be protected. Means are also provided for receiving the radiation energy reflected from the protected region. The reflected radiation energy is received between adjacent spaced transmitted pulses in the form of an AC analog signal at the given frequency, the peaks and valleys of which signal vary in amplitude with time. Means are also provided for allocating a portion of the time occurring between transmitted pulses into a plurality of time segments, each of which segments is long enough to correspond to a plurality of cycles of the analog signal.