Given this is Archie, if you can keep the cat flap locked while he learns about the bell, I am guessing he'll teach himself again!
My first cat, Mix, used to use the bell on his collar as a doorbell. He'd sit by the door (on either side) and scratch his collar so that the bell rang. When his collar, or just the bell, had gone missing, he'd jump up onto the windowsill and pantomime making his bell ring, while yowling to attract our attention. He was some cat.
(And yes, as catlovers already know, if someone was in to open the door for him, he would use the "doorbell" even when there was a catflap. Cat flaps are very undignified, y'know.

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