"No infrared isn't. I use the Predator style infrared. Think of that movie. It's based on heat. You can detect heat patterns even when something's invisible."
Bah, in your RPG an invisibility ring had better come with an Orca-Cola and a side of elven fries so the player who gets one feels they got something out of the deal ....
No, I also say that infravision is not on 100% of the time. You have to turn it on, otherwise I assume you're not using it.