Many power transformers are reaching the end of their useful lives. A utility then faces the decision of when to replace them. If the replacement occurs too soon this is financially inefficient, where the costs are ultimately passed on to the consumer. However if the utility delays replacement too late a failure may occur, resulting in an expensive and potentially dangerous situation. Determining an appropriate balance is challenging, and requires the monitoring of the power transformer fleet which is a complex task requiring a highly skilled professional workforce. Many different tests can be performed on a transformer. However, diagnosing a fault from a variety of results and making a condition assessment of the whole unit can be technically challenging. A transformer smart monitoring system, the SmartBox, has been developed at the University of Queensland (UQ) to provide an effective visibility of a transformer's condition from many different types of online and offline sensors, determine the life remaining of the winding paper insulation, and provide an overall health condition. The SmartBox comprises an industrial PC, measurement transducers and UQ developed software, and is designed to operate within the substation environment. The work that will be reported in this paper are the result of the experiences that industry partners Energex, Ergon Energy, Powerlink Queensland and TransGrid had with using this device. The SmartBox system monitors the parts of a transformer which have been found to be at highest risk of causing failure, e.g. oil quality and insulation condition. The SmartBox monitors these problems using: Dissolved Gas Analysis (DGA), Partial Discharge (PD), acoustic and vibration signatures, water activity of oil, and other various tests. The goal has been to produce a suite of algorithms, which diagnose the life remaining of the transformer and the propensity for failure of a component to occur.