an apparatus and method for waking up a main processor in a low power or ultra - low power device preferably includes the mp , and a sub - processor that utilizes less power than the mp to monitor ambient conditions than the mp , and may be internalized in the mp . the mp and sp can remain in a sleep mode while an interrupt sensor monitors for changes in the ambient environment . a sensor is preferably an interrupt - type sensor , as opposed to polling - type sensors conventionally used to detect ambient changes . the mp and sp may remain in sleep mode , as a low - power or an ultra - low power interrupt sensor operates with the sp being in sleep mode , and awakens the sp via an interrupt indicating a detected change . the sp then wakes the mp after comparing data from the interrupt sensor with values in storage or with another sensor .