If use use a phone :
• Google Pixel ( any version )
• Samsung Galaxy ( any version )
• LG watch sport ( any version )
Then don't turn your Bluetooth on because there is a new trick allow hackers access to your phone ( full access )
The trick is in Bluetooth Network Encapsulation Protocol and from this ( BNEP ) , hackers can access to your phone like an internet protocol ..
Google now work hard to fix this problem in Android Nougat 7.0 But not for older versions so just take care ..