Also - sorry for the double comment. The design was definitely influenced by similar form factor keyboards like the Op-1 and QuNexus although the latter does not use actual keys but is an MPC like pressure sensitive pad rather than a push/levered/actuated key. Also, in general, the design was influenced by the status quo of how producers / musicians approach such MIDI instruments and why/how they're used.
The biggest difference in our design is the exclusion of all controls, buttons knobs and so on which means that even though the Keys device is about the same size as some of these other portable devices, the keys themselves are nearly the same size and layout ratios as traditional. In other words, full size keys not mini size which is hard to tell in the pictures. This feature, of both our personal opinions and the feedback of professionals we gave Keys to, is significantly more important than any other in a truly useful as well as portable keyboard.
The fact that all controls are removed and the design is purely keys also allows for the modular nature, and the ability to connect Keys together in various ways as well as other modules.
The proximity sensor is indeed an IR based sensor similar in design to the D-Beam that Roland employs in some of their keyboards. The impetus for these sensors was the need to add a swipe gesture to transpose the keyboard up and down - the actual distance detection was a nice bonus which we exposed by it outputting control channel data.
Each sensor sends on a separate control channel, and when linking multiple keys devices together, the control channels are transposed so adjacent keys sensors each send CC on their own channel (so each sensor is mappable, and in the same fashion for a given configuration of devices)
The biggest difference in our design is the exclusion of all controls, buttons knobs and so on which means that even though the Keys device is about the same size as some of these other portable devices, the keys themselves are nearly the same size and layout ratios as traditional. In other words, full size keys not mini size which is hard to tell in the pictures. This feature, of both our personal opinions and the feedback of professionals we gave Keys to, is significantly more important than any other in a truly useful as well as portable keyboard.
The fact that all controls are removed and the design is purely keys also allows for the modular nature, and the ability to connect Keys together in various ways as well as other modules.