As cc on the A319 I can confirm the ding is connected to the retraction/extention of the gear. It happens at the same time as the exit sign stops/starts being illuminated. On descend it happens this way: landing gear goes down, about two seconds later 'ding' and exit signs illuminate. For cc it means now starts/stops the time of 'landing position'. And if the cabin is not secure yet, bloody hurry up! ;-)
For us to be released from our seats is a different 'ding' controlled by the flight deck, done with the seat belt sign and it only happens at the beginning of the flight not at the end.