A video surveillance method includes the steps of detecting, by a motion detector, an object motion, in the field of view of a surveillance device when the surveillance device is in a standby mode; generating, responsive to a positive detection to switch the surveillance device from the standby mode to an operation mode, one or more images of the moving object; determining, by processing the one or more images with a deep neural network (DNN) model of an object detector, whether the objects contained in the one or more images belong to a given categories, wherein the DNN model comprises N (N is a positive integer and ranged from 4-12) depthwise separable convolution layers; and video recording, responsive to a positive determination, the moving object in the field of view of the surveillance device.