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Require the least amount of cognitive overhead
A tea kettle can be set and forgotten, until it sings. It does not draw constant attention to itself until necessary. A tea kettle's whistle brings information from another room to one's attention.
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Provide information without distraction
An inner office window provides an understanding of whether someone is busy or not without the need to interrupt them.
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Compress information into other senses
Some products use buzzes instead of visual displays to present information or changes. These devices can convey the same amount of information without distracting the wearer or taking them out of their environment or task.
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Respect social norms and culture
Google Glass is an example of a fear-inducing technology. Placement of the camera at eye-level, cost, design, and its connection to a siloed, limited social network are both contributors to this social result.
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