The authors propose a low-power convolutional neural network (CNN)-based face recognition system for user authentication in smart devices. The system comprises an always-on functional CMOS image sensor (CIS) for imaging and face detection, and a low-power CNN processor (CNNP) for face verification. Implemented in 65-nm CMOS technology, the system consumes 0.62 mW to evaluate one face at 1 fps and achieves 97 percent accuracy.