| 摘要 |
A system (100) for detecting movable objects (102) comprises one or more devices (104) for detecting the movable objects (102). The device (104) has a detector (304) as well as an indicator (300) coupled to the detector (304). The detector (304) detects the arrival or departure of a moveable object (102) at a first location by detecting the attenuation of an electromagnetic signal, such as a radio signal. The system (100) can use Global Positioning System (GPS) transmissions, but in the preferred embodiment, the system (100) uses terrestrial Global System for Mobile communications (GSM) signals. |
