You have 3 attempts to enter the correct code. On the 4th failed attempt, the radio will lock for 1 hour (display "SAFE" and a countdown timer). Do not turn off the ignition during this lockout period; leave the radio on until it resets.
: On some RCD 300 models, you can display the serial number by pressing and holding buttons 1 and 6 simultaneously for several seconds.
If your radio displays "SAFE" on the screen: