HKPAX,
On Airbus's (330 & 340, can't say for sure on other types), the first gong will be confirming the gear is up. On approach, you will also hear a gong when the gear is down and locked.
After the VS24 incident in '97 (wasn't on it, but knew crew that was) I did spend time on my first few A340 flights afterwards listening for that 'down and locked' gong whilst holding my breath!!!
Cheers,
Bob