Power consumption of a circuit which makes a determination is reduced. The accuracy of a system which makes a determination is improved. The safety of a target object which is monitored by a sensor element is increased. A system which easily monitors a target object is provided. A semiconductor device includes a detection circuit having a function of analyzing first data and making a first determination of selecting a first value or a second value, a first determination circuit and a second determination circuit having a function of performing feature extraction of an image, a power supply circuit, and a power management unit. The power management unit has a function of allowing a voltage to be supplied from the power supply circuit to the first determination circuit in the case where the first value is selected by the first determination. The first determination circuit has a function of analyzing the first data and making a second determination. The second determination circuit has a function of analyzing the first data and making a third determination in the case where an occurrence of an event is detected in the second determination.