US Patent 7302089 Autonomous optical wake-up intelligent sensor circuit

Devices, modules, and methods enable a mobile device to change from a standby mode with low power consumption to an active mode with relatively higher power consumption, upon recognizing that a received image is substantially similar to a visual signature. The visual signature is based on an image, such as the face of the intended user, is stored in a memory. When later the mobile device is in the standby mode, it periodically performs a low power peek with a camera to receive an image of the area in front of the mobile device. If the received image is recognized as substantially related to the visual signature, the mobile device is enabled to change from the standby mode to the active mode.