Identify this bathroom light switch?
It turns out it was a Wattstopper PW-301-LA Motion Sensor, Passive Infrared Wall Switch.

You reprogram it for auto-on by flipping dipswitches underneath the power button. The PIR window is hidden in the lower third panel. The default is manual-on (PIR off) per CA electrical efficiency requirements so I don't think I'll change it. 

The manual is on the manufacturer website.