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In this paper, analytical and experimental results on fluxgate magnetometers, intended to sense dc magnetic field, that make use of a readout technique based on the estimation of the residence times in the stable attractors are presented. The approach, exploiting the inherent nonlinear character of the bistable core dynamics, is based on the time-domain characterization of the transitions between the two saturation states of the hysteresis loop that is inherent in the ferromagnetic core dynamics. This readout technique affords the possibility of low amplitude and frequency reference (or bias) driving signals (sinusoidal or triangular), compared to conventional fluxgates, thereby reducing the device power requirements. The efficacy of this strategy is shown through an analytical approach, and via experimental results that suggest guidelines for the optimal design of the device. Considerations of the effects of a suitable choice of the magnetic core (in terms of its hysteresis behavior) have also been included. Experiments, carried out on miniaturized laboratory fluxgate prototypes with different ferromagnetic materials, reveal good performances of the proposed methodology, including suitable sensitivity and resolution, as well as low cost.