They’re the kind of features that nobody warns you about, even Apple doesn’t. It’s actually one of those hundreds of new features that the new operating system has that are not even mentioned in the Keynote, but it has a very ingenious way of working. And the reality is that it is very useful.
The mechanism is very simple. If you have a Mac, as you may know, the iSight camera is located on the top edge of the monitor. The camera is there, whether it’s on the MacBook, the iMac, or the Cinema Display. To its right, as you look, is the light that indicates its status, when it’s working. To the left is the brightness sensor that controls the brightness of your display or the backlit keyboard .
This has been discovered by a user who has been “entertained” by studying the Mavericks code. The system takes advantage of the computer’s ambient light sensor for more than just controlling the brightness of the screen. When we move in front of it, we cause variations in the ambient light that the sensor detects.
Every time it detects a variation, the system resets an internal timer . This way it can monitor when someone is sitting in front of the Mac, even if they are not doing anything on it, it simply knows that they are there .
This prevents the computer from going into sleep mode. So, for example, we can read something on the screen (or some document in front of us) without the computer turning off the screen.