| 摘要 |
A monitoring system uses a portable master unit and at least one portable slave unit. The master unit provides an electrical circuit including an antenna, an RF signal amplifier, an RF signal tuner, a countdown timer, an attenuator, an adjustable delay timer, an AND gate and an audible alarm. Each of the slave units providing a slave circuit including a transmitter with transmitting antenna and an RF pulse generating circuit. The master unit is adjusted for receiving RF energy transmitted by a slave unit when the units are separated by a target distance or less. A time delay parameter is set using dual timers so that the slave may be positioned beyond the allowable distance parameter for a pre-selected duration before the alarm is triggered.
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