One embodiment of the present invention relates to a method and apparatus to perform a low power activation of a system by measuring the slope of a digital signal corresponding to a motion sensor measurement value. In one embodiment, a low power activation circuit is coupled to magnetic motion sensor configured to output a magnetic signal proportional to a measured magnetic field. The low power activation circuit may comprise a digital tracking circuit configured to provide a digital signal that tracks the magnetic field and a difference detector configured to detect a difference between a current digital signal and a prior digital signal stored in a digital storage means. If the detected difference is larger than a digital reference level, an activation signal is output to awaken a system from a sleep mode.