Why you need to double check your iPhone Bluetooth settings
Recent iOS updates have automatically re-enabled Bluetooth for many users who keep it turned off for battery conservation or privacy reasons.
The increasing use of iBeacons and other Bluetooth based tracking systems make this a bigger privacy worry than before. Tracking via Bluetooth is now a widely and actively used tool in retail and other areas.
Conspiracy theorists suggest that Apple is doing this intentionally to increase the usefulness of iBeacons to track people, and thus encourage their adoption. While this is an appealing idea, the jury is still out on this one.
If you are concerned about this kind of tracking, you can quickly disable Bluetooth in the control center on your iPhone by sweeping up from the bottom of just about any screen and tapping the Bluetooth button. It is fairly easy and convenient to keep Bluetooth turned off most of the time, and just enable it when you want to use a wireless headset or other Bluetooth device for a short while.