Very difficult to say with any certainty without seeing the vehicle, but the first thing i would suspect would be the door switch circuit. does the dome light illuminate when you open the door? it is the same sensor that signals the dome light as that signals the buzzer for the lights when you open the door. in hondas, with the key off but the key still in the ignition, there should be a green key image illuminated on the instrument panel. if that is not illuminating, there could be a problem with the ignition switch. hope thats helpful, its really the best i can think of without seeing the vehicle! good luck!

Your buzzer may not be activating due to a bad door switch. The buzzer on any vehicle rarely ever goes bad and if it does, this is a dealer part.
The switch looks like the one pictured below. If I may recommend a solution; Let it go, don't bother with an expensive repair to resolve this problem. Just be alert to turn the lights off and remove the ignition key.
Vehicles of earlier production did not have this option, and it seems wew were all ok without it....No? Just a thought to save an expensive repair bill.