Abstract: Apparatus and methods for non-invasively determining a temperature of a fluid inside a housing are provided. First and second temperature sensors are positioned so that there is a temperature differential between the first and second temperature sensors. A difference between the temperature of the first and second temperature sensors can be used to estimate the temperature of the fluid inside the housing and/or a zero heat flow methodology can be used to determine the temperature of the fluid inside the housing.

Abstract: The present invention is directed to a system for determining content level in a fluid holding tank and requesting refills. One embodiment of the system comprises a magnet that produces a magnetic flux around a housing for an existing content level gauge, a Hall Effect sensor transmitter unit disposed on the housing and having at least one current detecting loop therein for detecting any variation in a magnetic field created by the magnet, and a metal content level gauge disposed within the housing. The degree of variation corresponds to a measured content level as indicated by a position of the metal content level gauge. The system further comprises a base station receiver transmitter unit for receiving a signal from the Hall Effect sensor transmitter unit and forwarding that signal to a remote registry.