At that point, just use Morse code. For small buildings, the cuckoo clock method works too.

the main reason why elevators in Hong Kong do not is that most of them are high speed high-rise elevators and the numbers just whip by. It would probably be very frantic sounding to use Morse if you went from ground to 50 in less than a minute.

Instead they only announces floors that are stopped on, so this works fine.

One benefit of using spoken vernaculars rather than Morse is that Morse has to be taught; Hong Kong historically draws large portions of its population from migrants originating from all over China, where until recently there was wide variance in schooling and literacy rates.