Let me clarify, apologies if I was sloppy in my OP. As ma smith said, lasers and IR illuminators are definitely part of it, but I also recall reading a long while ago already that scopes that electronically enhance the ambient light can also be picked up by various night vision mechanisms. I don't recall the specifics as it was something I was looking at in the 1990s when I lived and worked in a country and worked in a job where that could have been a concern. Not an issue today, but the geek in me wanted to recapture some of the information I lost in various moves across countries and continents. A recent conversation with a military sniper in passing seemed to confirm that this was a thing he was aware of too. I didn't think to ask him more about it at the time, but later it got me wondering about the specifics and what technology has done since. I know there are very many options available today that were just not around in the 1990s and I have not kept up. As I am now retired, I got curious.