Vague Senses
Source Player Core pg. 424
A character also has many vague senses—ones that can alert you that something is there but aren't useful for zeroing in on it to determine exactly what it is. The most useful of these for a typical character is the sense of smell. At best, a vague sense can be used to detect the presence of an unnoticed creature, making it undetected. Even then, the vague sense isn't sufficient to make the creature hidden or observed.
When one creature might detect another, the GM almost always uses the most precise sense available.
When one creature might detect another, the GM almost always uses the most precise sense available.