This achievement is pretty easy to miss.

And you have to do it in one playthrough.

So I want to help anyone who might have just missed one character, which can be very annoying.

Download my save package using the following link:
https://drive.google.com/drive/folders/11uYA1I8OWuJa3-sYzldCxBdoZz4AUWPC

Unzip the ZIP file and copy the saves to the following Windows directory:

C:\Users\%USERNAME%\AppData\Roaming\Revolution Software\BS1R\

CAUTION!!! Better deactivate cloud synchronization in Steam and make a backup of your own saves.

Then start the game and load the last save. It should be manual save 20.

Talk to the guy to your left and select the buzzer in your inventory.

After this conversation, the achievement should be unlocked.

I haven't tested this further, so please let me know if it doesn't work.

Also a side note...
I really just want to help with this particular achievement. Do yourself a favor, play and enjoy this classic.
You can see how much love was put into this remaster, and if we continue to support this team, hopefully more good point & click adventures will be produced with George and Nico.