The Si115x is an active optical reflectance proximity detector, with ambient light sensors whose operational state is controlled through registers accessible through the I2C interface. The host can command the Si115x to initiate on-demand Ambient Light or proximity measurements. The host can also place the Si115x in an autonomous operational state where it performs measurements at set intervals and interrupts the host either after each measurement is completed or whenever the sample is larger/smaller than a set threshold value or exits/enters a set threshold window. This results in overall system power saving, allowing the host controller to operate longer in its sleep state instead of polling the Si115x.