Extrasensory

"Extrasensory" monsters are monsters that do not rely on sight to detect other characters. They might be able to smell, or even sense you through some other means, allowing them to target and attack you even when you are hidden or stealthed.

You can detect extrasensory monsters through analyse (which does not break invisibility or stealth). Monsters that can see you have an "Extrasensory" flag in the analysis result.