Sorry to be so cheeky and submit this as an answer but I think you have it spot on already....anti-hostage doesn't ring.
I know (and I'm sure you do as well as you live in Spain) that many banks here have those security doors which mean that a member of staff has to push a button to allow entry from the street, thus preventing masked, potential robbers entering. However it does nothing to prevent a potential hostage situation if the robber is not bothered about showing his identity to the door's security camera. What I'm trying to say is I don't think your ST has anything to do with the Spanish security doors - does it?
I think the part about "coaccio'n" confirms your own translation - it's a silent trip switch / panic button, e.g. if the manager is taken out of office hours and forced (coersed) into entering security numbers - there is also a password ("contrasen'a pactada")which sets off a silent alarm / connection with the police.
Hope this helps, sorry again for cheekily giving your own answer ;~)