Android 4.3 WiFi Always-On Feature
Updating to Android 4.3?
You may want to dig a bit deeper in your phone's settings menu.
A new, slightly hidden feature in Google's latest Android flavour is Always-On WiFi Scanning.
"Always-on" as in "even when you (think) you turned WiFi off" via the usual toggles.
The feature, so Google, serves "To improve location accuracy and for other purposes, Google and other apps may scan for nearby networks, even when Wi-Fi is off".
"Other purposes" could mean all kinds of things, of course.
So, if PRISM and other security and privacy concerns have already pushed you close to the edge, find out how to disable Always-On WiFi Scanning here