Abstract: A low power flow measuring apparatus, including a battery for generating a supply signal, a power management unit for producing from the supply signal a first voltage signal that is always enabled and a second and third voltage signal that are selectively enabled, a sensor powered by the third voltage signal for generating a data signal representative of a magnitude of a predefined parameter, and a controller in communication with memory and the sensor and powered by the second signal, for controlling a reading of the data signal from the sensor and the storage of a data value corresponding to the data signal in memory. Interrupt logic, powered by the first voltage signal, activates the power management unit, upon the occurrence of a predefined event, to enable the second and third voltage signals, thereby enabling the controller to take a reading from the sensor. After a reading is taken and the data value written to memory, the power management unit disables the second and third signals to save power.