A system for alerting a golfer when the golfer has moved too far away from his golf club. One or more clubs are provided with transmitters which transmit on a specific frequency and may contain digital encoding. A common receiver is used to detect the signal from one or a plurality of transmitters. When...http://www.google.com.hk/patents/US5952921?utm_source=gb-gplus-share專利 US5952921 - Misplaced golf club reminder
