An ambulatory monitoring device includes a sensor to monitor a physiological signal and a battery power source. The device also includes a wireless receiver adapted to monitor a first frequency band having frequencies below 1 MHz and configured to detect and receive, using less than 10 micro-amps of current from the battery power source when operating, wireless communications within the first frequency band from a remote device at least one meter away. The device further includes a wireless transmitter adapted to transmit—after receipt from the remote device of a first wireless communication within the first frequency band that includes an invitation for further communication—a second wireless communication in a second frequency band having frequencies above 10 MHz, the second wireless communication comprising data indicative of the physiological signal as sensed by the sensor.