California Vehicle Code:
(a) A person shall not drive a motor vehicle while using an electronic wireless communications device to write, send, or read a text-based communication, unless the electronic wireless communications device is specifically designed and configured to allow voice-operated and hands-free operation to dictate, send, or listen to a text-based communication, and it is used in that manner while driving.
(b) As used in this section "write, send, or read a text-based communication" means using an electronic wireless communications device to manually communicate with any person using a text-based communication, including, but not limited to, communications referred to as a text message, instant message, or electronic mail.
(c) For purposes of this section, a person shall not be deemed to be writing, reading, or sending a text-based communication if the person reads, selects, or enters a telephone number or name in an electronic wireless communications device for the purpose of making or receiving a telephone call or if a person otherwise activates or deactivates a feature or function on an electronic wireless communications device.
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I'm sure the courts will classify the Apple Watch under this code. And to be honest, I'm okay with that, because there are enough horrible drivers here in SoCal.