Possible features for Apple Glass include a self-cleaning feature and a 3D audio feature that navigates with sound, according to Apple's patent application documents.

According to Apple Insider, Apple has filed an application with the USPTO for a system titled "Audio-Based Feedback for Head-Mountable Device." It uses multiple microphones that detect even sounds that one's ears would have trouble picking up. And future smart glasses could provide visual indicators to guide the user to the source of the sound.

The rumored Apple Glass is nowhere to be found. But this feature was clearly conceived with smart glasses in mind, as the lenses could display these visual notifications as part of a heads-up display.

The idea of using a microphone that can detect sounds outside the normal hearing range suggests a navigation purpose behind this feature. Nevertheless, this feature also has potential as a hearing aid, providing a visual warning of closer sounds, such as traffic noises or shouting.

In addition, an older patent points to the possibility that Apple Glasses could use on-board speakers to create realistic sound effects in conjunction with visual elements. In other words, the glasses could even play a composite of sounds that cannot be heard by the user but can be detected by the microphone.

Apple is also considering making Apple Glass self-cleaning. Another USPTO application document titled "Particle Control for Head-Mounted Devices" describes "an optical module that removes particles from the optical path and traps particles so that they do not obstruct the user's vision.

This sounds even more futuristic than 3D audio, and the patent does not fully explain how such a module would remove dirt from the Apple Glass lens. The closest it comes is a reference to an actuator device that "vibrates the display element," which would likely work by shaking dirt off the Apple Glass by vibrating the lens.

While it all sounds very fancy, these are just the latest cutting-edge features rumored for Apple Glass. Others include a zoom-style background for the display and enhanced low-light vision. Meanwhile, one leak suggested that Apple Glass would use the iPhone screen in a similar fashion to Google Cardboard.

At this point, it is safe to say that Apple is currently working on Apple Glass. However, we will have to wait and see which features will eventually make it into the final product.