Key dates...
For individuals born in or after 1970 who have not replaced their old Hong Kong ID card, they must renew their smart identity cards by May 12, 2025. After this date, the old ID cards will be considered invalid.
For those born on or before 1969, their old HKID card will become invalid on October 12, 2025.
The department estimates that most of the 182,000 people who have yet to register for the new smart ID cards are likely overseas.
I passed through HK immigration a few weeks ago with my old HKID. I guess after May next year I should hide the ID from the immigration officers to avoid it getting confiscated.