Of particular concern are newer Android gadgets, specifically those running Android 3.1 "Honeycomb" or later. That version of the Google OS introduced a feature called Preferred Network Offload (PNO), which has a habit of broadcasting the names of the last 15 Wi-Fi networks a device has joined, even when the screen is off.

The idea is to conserve battery by allowing a phone to connect to known Wi-Fi networks even while in sleep mode, since Wi-Fi uses less power than the mobile data radio. The problem, the EFF says, is that your wireless network history can give a worryingly accurate and thorough picture of your movements.