Let's start with communication and bit more special non-verbal interfaces.

1) For people not able to communicate there are a lot of gaze techniques. It means that you have to choose from letters or symbols with your eyes.
One electronic version keeps complete sentences saved with a unique key each.

For example: ...is operated by triggering the clock hand to sweep around and point to the desired picture, word, or object affixed to the clockface. This model has single or double switch capability. One switch moves the hand clockwise, the second switch moves it counter-clockwise. The transparent face of the clock was designed to allow the child and teacher/therapist to view each other and encourage face-to-face communication. This is build for childs as a toy to learn how to use gaze methods but i can imagine a lot of fun toys out of this idea.

Another example is computer based:

Users make selections by looking at keys displayed on the screen for a fraction of a second. A small camera mounted under the Eyegaze screen takes 60 pictures per second of the user's eye. Those images are analyzed by a processor that interprets where the user is looking. Users generate speech by using an on screen keyboard or pre-programmed phrases. Various options permit the user to turn on lights and appliances and access any personal computer as a keyboard and mouse interface for email and internet access. Nothing is attached to the user, and the system comes with a flexible mount that enables people to use it from any position...

Another device that works on eye position control is the Visionkey.

The selected characters appear on the Display Unit and are forwarded to an optional computer. The equipment consists of an eyepiece mounted on standard eyeglass frames, linked by a cord to a book-sized Display Unit having a 20 character display on each side so that both the useer and the correspondent can read the message while they face each other. VisionKey allows you to use standard office software and unlike voice recognition systems, it allows you to work in noisy environments without the possibility of being overheard.

What is a good example how those technologies can be used in "normal" environments. And other way round if you see the Carrying appliances you understand how "wearable" would help.

Picture: Assistive Technology Services (ATS)