There have been strict laws all over Australia - not just Melbourne.
Here is the smallest Swiss Army knife available these days -
it would fit nicely on your keyring – sold at Bunnings -
Blade length is 34 mm or 1.33 inches.
https://www.bunnings.com.au/victorinox-classic-sd-pocket-knife_p0493747It is illegal to have that in Victoria – even on the keyring for your car keys.

A long time ago I was going through Brisbane airport and I had a similar
one – maybe even smaller – on my keyring and it was found when they X-rayed
all my pocket contents on their airport security conveyor.
They confiscated it.
Later that month I saw a TV article about Brisbane airport and they had
a large container- maybe 2 cubic meters and it was full of pocket knives
that they had confiscated from members of the public.
My point is that all knives have been illegal for a long time
to carry in public – in fact -
I believe you can't even have one
in your toolbox in the boot of your car?