[user24]

The mic issue is actually more worrying, but as you point out, there aren't such easy solutions.

[eliasmacpherson]

Hacksaw a 1/4 inch jack, insert. Disable what you can at software level, remove drivers/codecs for recording. Not easy though.

[user24]

"iMac has two built-in microphones"

https://www.apple.com/imac/features/

So that won't work for me, sadly.

[eliasmacpherson]

i'm sure there are some environments that have strict no mic's requirements, i wonder what they do to disable mic's on the iMac. Perhaps they don't use iMacs or disable sound in the bios?