An RFID reader requires significant power supply current, upwards or beyond 0.5 amps. Much of this power is expended to activate the reader's radio frequency transmitter. For example, the reader's transmitter may constantly be active awaiting a RFID tag entering within its electromagnetic field. Sometimes an adequate power source, such as AC mains, is not available to provide continuous operation and instead a battery is powers the reader. This invention detects that a RFID tag is within reader range without using the reader's RF transmitter at full power. As a RFID tag is brought within range of a reader's antenna there is significant mutual inductance coupling between the tag antenna and the reader's antenna and this invention provides a sensitive detector of this mutual inductance. The detection of mutual inductance automatically triggers the reader's transmitter to a higher power which is necessary to fully activate the RFID tag.