The present invention concerns a device and a method for controlling the operating state of a low power electronic system powered by an electric power source (5) and including in particular a microprocessor (10) able to operate at a guaranteed minimum operating level (V[err]). A reset signal (CPU RST) keeps the microprocessor 5 in a reset state is supplied as long as the supply voltage (V[err]) supplied by the power source is lower than the guaranteed minimum operating level. According to the present invention, the reset state of the microprocessor is kept as long as the supply voltage is lower than a power-on-reset threshold (VPOR) which is, or may be lower than the guaranteed minimum operating level, and this reset state10 is extended beyond the power-on-reset threshold as long as the supply voltage has not at least reached the guaranteed minimum operating level. Consequently, the lifetime of the power source is increased and the microprocessor is prevented from executing erroneous instructions when the latter is in the "grey zone" defined by the range of voltages between the power-on-reset threshold and the guaranteed minimum15 operating level.
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