Back in May, the US Patent and Trademark Office approved an interesting Apple patent, one that will allow (if Apple does in fact implement it, which is likely) the iPhone to automatically adjust its volume based on its proximity to your face. There are many reasons why that could prove to be a useful feature, and it's now become clear that Apple had no intention of stopping there with this basic premise.
Today, we can see that Apple had actually applied for a similar patent mere months before the aforementioned one was approved; this time, it involves earbuds. According to the patent, volume would be adjusted based on how sealed the earbud is in the ear, which should help prevent "audio leak" that some older Apple earbuds suffered (much to the annoyance of anyone around you).
In addition to simple volume adjustments, this technology could also tweak the equalization settings, adjust noise-cancellation properties and perhaps most interesting of all, can do so on a per-earbud basis - effectively, the left earbud could produce a lower volume than the right if it's not as well sealed in your ear.
As hinted in the patent, the device's software could be used to notify the user about an inadequate seal, issuing a simple error: "Your earbuds are not seated properly, please adjust for optimum sound quality". I'd prefer something akin to, "Your earbuds are not in your ears; look around, does anyone notice?" Apple, you can have that for free.
One thing that's not mentioned in the patent is whether or not the technology can be disabled. Since it's highly likely to be software-driven, there wouldn't be any reason to not give people the option, should they want it, so hopefully we'll see that happen.