I just updated to MIUI 2.4.20 and attempted to pair with my car's bluetooth system. This was working perfectly with the same system and phone running MIUI 2.4.6. I'm using an MI-ONE. The car system requires the pairing to be initiated by the phone as follows. 1. Enter pairing setup in the car system 2. Define 4 digit pairing code in the car system (must be 4 digits) 3. Make phone BT visible 4. Pair the devices using the phone's pairing function and the pairing code defined in the car system at step 2. The problem occurs at step 4. The MI-ONE is indicating High Security Enabled: Needs 16 character key. So when entering the pairing code in the phone, the 'OK' button is greyed out unless you enter 16 characters. This won't work because the car system limits me to a 4 digit pairing code. Noting that MIUI 2.4.20 is ICS 4.0.4, maybe some new BT funcitonality has been implemented to support "High Security" bluetooth. If this is the case, either the car system is bugged (reports high security to the phone but limits the code to 4 digits) or the phone is incorrectly identifiying the car system as requiring the 16 digit code. Incidentally, I've been able to pair the phone with other devices (Windows 7 PC, S60 phone and Honeycomb/ICS tablets) using normal paring codes (not 16 digits).