Abstract: Provided is a sensor operative to track changes in a liquid level of a hand-held liquid container, the sensor comprising: an ultrasonic liquid-level sensor configured to indicate a liquid level of a liquid in a hand-held liquid container, wherein the ultrasonic liquid-level sensor is capable of indicating the liquid level when the surface of the liquid is less than 20 centimeters away from the ultrasonic liquid-level sensor; a radio transmitter; and a processor configured to draw power from a portable power source, receive liquid-level indications from the ultrasonic liquid-level sensor, and cause the radio transmitter to transmit data indicative of changes in the liquid level.

Abstract: Provided is a sensor operative to track changes in a liquid level of a hand-held liquid container, the sensor comprising: an ultrasonic liquid-level sensor configured to indicate a liquid level of a liquid in a hand-held liquid container, wherein the ultrasonic liquid-level sensor is capable of indicating the liquid level when the surface of the liquid is less than 20 centimeters away from the ultrasonic liquid-level sensor; a radio transmitter; and a processor configured to draw power from a portable power source, receive liquid-level indications from the ultrasonic liquid-level sensor, and cause the radio transmitter to transmit data indicative of changes in the liquid level.