An electronic device receives depth sensor data that includes depths sensed in multiple zones in the field of view of a depth sensor. The device determines whether a user is in front of the device based on the depth sensor data. If the user is determined to be present, then the device causes a display to enter an operational mode. Otherwise, the device causes the display to enter a standby mode. The device may also determine whether the user's attention is on the device by determining whether the depth sensor data indicates that the user is facing the device. If so, the device causes the display to enter the operational mode. Otherwise, the device causes the display to enter a power saving mode. The device may use a machine learning algorithm to determine whether the depth sensor data indicates that the user is present and/or facing the device.