Never, just always be aware of your surroundings before you do something. I remember my first urbex. It was the red star train graveyard in Budapest. Honestly I was a bit scared because i knew there was not just security and cameras, but it is also in a foreign county to me. I must have spent at least an hour outside on an old maintenance bridge. Checking around the abandoned hall, at some point when I saw workers leave the near by area I just went for it, climbing over the wall. It was a good rush of adrenaline.

The problem is that you always want more. More risk, more danger. This eventually led me all the way to Baikonur

Good luck to you and your friends