Morning lookout I don't think it must have been as Caroline was insisting Vidvic gave her proof of its existence and she was told she would have to take his word for it had it been mentioned at Trial he would have known about it.
Morning Susan,,,it looks bad on the relatives if they've been insistant about a panic-button being there and Neville not being able to get at it. That in itself puts Jeremy in the frame as him being the perpetrator by restraining his father in such a way that he couldn't summon help.
So it would be made obvious to everyone that indeed a panic-button had been installed.
Was it installed afterwards to look as though it had been there all the time.?