- It must be useful, and this usefulness must be measurable.
- The less interaction required, the better. For example, why use both hands when you can use just one.
- Device should not disturb you from daily tasks.
- It must be safe to wear.
- Device must be easily extensible.
- On software level:
- It should be relatively easy to write your own extensions.
- The only thing required to change the client code is a text editor. By using interpreted languages we can make it possible to edit the code as soon as you get some idea.
- On hardware level:
- Ring, SPI and !I²C ports to allow pluggable modules.
- Excessive hardware features. Things like barometer or accelerometer are not required for basic functionality, but they provide freedom of thought for developers.
- All development files must be released under free software license. Besides boosting development speed by letting others to contribute, these files might come handy for other projects.