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Apple Patent 20130044215 for "Wearable Accessory Device" (2011)
In 2011, Apple filed a patent for a "Wearable Accessory Device", #20130044215.
While there is no proof any of this will be integrated in Apple products anytime soon, it's definitely an eye opener into future wearable computing developments at the company.
SONY MN2SW Android Watch (2012)
Released early summer of last year, SONY has the first "Watch companion" released into the wild with its MN2SW, which requires an Android phone with a Bluetooth connection.
For a review, check out CNET's in-depth look at the device.
Pebble, a new startup company, will soon be offering its low-power, E Ink-based bluetooth watch companion for iOS and Android smartphones in April-May of this year. The device will cost $150. The device contains a motion sensor and can run simple apps that display telemetric-types of output from data coming from connected Smartphones.