Honda radios unlocked online — from the serial printed on the unit’s casing.
A Honda head unit asks for its code after any loss of power — a flat battery, a jump start or an alternator change is enough.
The serial is on the label on the casing, so the unit has to come forward out of the dash; most are held by screws behind the trim panels rather than by release keys.
On the label look for the 14-character string starting HO. Ignore the Honda part number — that names the model, not your unit.
We have no code from a Honda owner confirming the rule yet, so this one is free: a share unlocks it, and your answer about whether it worked is what moves Honda into the confirmed column.
Serial number example:
HO652FA9000039