| 摘要 |
<p>A system for locating movable objects and detecting the failure of the object to visit a designated area within a predetermined time, including a base unit (10), a transceiver (12) attached to the movable object (22), and a portable locating device (32) having a directional antenna. The base unit (10) includes a transmitter circuit (14) which generates a first signal (16) for substantially continuous transmission within a zone (18), which encompasses the designated area. When the movable object (22) enters the zone (18), the receiver portion (48) of the transceiver (12) receives the first signal (16) and resets a timer (58) within the transceiver (12). If the movable object (22) fails to revisit the zone (18) within the predetermined time, based on predictions of the movable object's movements, the timer (58) times out and switches the transceiver transmitter (52) into an active mode wherein the transceiver (12) emits a second signal (26). The second signal (26), which may contain information identifying the movable object (22), can be detected by using the locating device (32) to track down and recover the movable object (22). In an alternate embodiment, a fixed mast-mounted locator receiver (34) detects the second signal (26) and provides information regarding the approximate location of the movable object (22).</p> |
