The iPhone’s auto-volume sensor: How do it know? - Macenstein

The iPhone’s auto-volume sensor: How do it know?

Posted by Dr. Macenstein

Here’s something cool I just noticed about my iPhone. It apparently can remember the volume you last set when using the headphones as opposed to a car or stereo, and it will auto adjust accordingly.

Because of the iPhone’s recessed ear piece jack, I had to buy a $10 Belkin Headphone Adapter in order to listen to the iPhone in the car (works great, by the way). When I listen to the iPhone in the car, via my Aux input, I have the iPhone’s volume set to 100%. However, I noticed that when I unplug the Belkin adapter, and plug in the iPhone’s standard headset, the volume slider automatically slides back down to 50%, the volume I have set for headset listening. I thought that was pretty cool, and tested the other way. Sure enough, unplugging the headset, and replugging in the Belkin brought the iPhone volume back up to 100%.

So how do it know?

Well, odds are the Belkin adapter is a standard mini stereo connector (without the iPhone headset’s ability to transfer voice) so the iPhone must be able to sense that. If this is an intentional feature Apple threw in, kudos to them. I understand this probably isn’t a big selling point that will make people rush out to get the iPhone, but I still think it’s a nice touch and something the world should know.

Of course some would argue Apple might have included a few other features ahead of this one.

[UPDATE: Well, it seems that what the iPhone is actually doing is remembering your volume settings for both the headset and for the “speaker” volume. If you pull the headset out of the iPhone while it is playing, you’ll see the slider move to the last volume you had the speaker set to. Apparently the iPhone considers any device other than the default headset to be an external speaker, so that’s why playing out of the Belkin adapter also changed the volume level.]

[UPDATE 2: Faithful Macenstein reader flynn has pointed out my ignorance. Apparently this is a feature of OS X and works on laptops. It seems to just have been carried through to the iPhone’s version of OS X as well.]

4 Responses to “The iPhone’s auto-volume sensor: How do it know?”
  1. flynn says:

    Newsflash: That’s Mac OS X. Works the same on a laptop and on a phone…

  2. Thanks flynn. It actually WAS a newsflash to me, as I don’t use a laptop.
    Oh well.

    -The Doc

  3. jt says:

    If you look at the plug on the iPhone earbuds, you’ll notice there are 4 contacts as opposed to 3 on a standard stereo phono plug (left channel, right channel, and common ground) The 4th contact has a dual purpose – for both the mic and the switch on the wire. When they’re plugged in, it must complete a circuit that tells the phone that they’re plugged in

  4. Ryan says:

    I want to know why my SIK IMP doesn’t work with my iPhone. ( )

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