Screen-less wearable devices allow for the smallest form factor and thus the maximum mobility. However, current screen-less devices only support buttons and gestures. Pointing is not supported because users have nothing to point at. However, we challenge the notion that spatial interaction requires a screen and propose a method for bringing spatial interaction to screen-less devices.

We present Imaginary Interfaces, screen-less devices that allow users to perform spatial interaction with empty hands and without visual feedback. Unlike projection-based solutions, such as Sixth Sense, all visual "feedback" takes place in the user's imagination. Users define the origin of an imaginary space by forming an L-shaped coordinate cross with their non-dominant hand. Users then point and draw with their dominant hand in the resulting space.

With three user studies we investigate the question: To what extent can users interact spatially with a user interface that exists only in their imagination? Participants created simple drawings, annotated existing drawings, and pointed at locations described in imaginary space. Our findings suggest that users' visual short-term memory can, in part, replace the feedback conventionally displayed on a screen.