One of the things that keeps some people from cycling more often is the gears – although they need the gears to manage hills and headwinds, they're never sure which one they should be in. If that sounds like you, then you might like the Autobike. It shifts gears automatically based on the rider's cadence, and manages to do so without a battery.
Instead of a battery, the Autobike has an SRAM Dynamo front hub. This uses the spinning motion of the front wheel to generate electricity, which in turn powers the bike's electronics and gear-changing servo motor. The electronics measure the rider's cadence via a number of sensors, and activate the motor to automatically shift the bike to a higher or lower gear in order to maintain that rhythm.
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Also included in the electronics package is an accelerometer, that can detect when the bike starts going up an incline. When that happens, a lower gear is preemptively selected.
Because the Autobike has a continuously-variable Nuvinci N360 rear hub transmission, the rider won't notice any kind of transition between gears – in fact, technically-speaking, they'd be better described simply as drive ratios.
Not everyone wants to pedal at the same rate, however, so users can chose between three pedaling speed ranges. This can be done using either a set of buttons mounted on the down tube, or wirelessly via a smartphone app.
The Autobike is currently available in two commuter-style models, the Voyage and Voyage ST, which sell for US$1,000. A hybrid model, the Evolution, is due to be out soon.
There's more information in the video below.
UPDATE (Sept. 22/13): One of the Autobike's creators has informed us that the three pedaling speed buttons are actually used to adjust the cadence in 5 rpm increments (up or down) per push, allowing the rider to maintain a cadence anywhere from 30 to over 100 rpm.