The very first Glass prototype, which wasn't shown off, was essentially just a big screen twice as big as a human face; it featured a coat hanger and a pico projector. Not a practical solution, of course, and definitely not a portable one. So the Google X team came up with the Pack (seen above), which only looked slightly less ridiculous. This handy model used a backpack with a laptop, GPS and mobile keyboard, and it came with a webcam, earbuds and Samsung smartphone, which was solely used as an early version of the Glass trackpad. Yes, this meant that testers walked around in 2010 with a phone attached to their cheek and a pack strapped to their back.
Fortunately, most prototypes actually improve as time progresses, and that's exactly what happened with Glass. The Cat model, which came out the following year, shed the backpack and smartphone. Instead, the 3D-printed frame had Nexus 5 guts grafted onto the right side along with an awkwardly placed battery on the left. Curiously, the optical display sat underneath eye level. Cat was heavy, but it was at least the first truly portable version of the wearable.
Finally, the Emu model came later in 2011. Once again, it was a significant improvement in looks, weight and portability: It was cleaner, the circuitry wasn't as rudimentary as older models, the optical display was positioned above the eye and it came with a bone conduction speaker that hung out on the back of the head.
I/O didn't provide us with any new details about the consumer-facing future of Glass, but at least we got to know a bit more about its past.