Scrying

A scrying effect creates an invisible magical sensor that sends you information while the effect lasts. Unless noted otherwise, the sensor has the same sensory abilities that you have naturally, but not any sensory abilities you gain from other spells or technology. The sensor is a separate, independent source of sensory input for you, and thus it functions normally even if you have been blinded or deafened or otherwise suffer sensory impairment.

A creature can notice a scrying sensor with a successful Perception check (DC = 20 + the spell or effect’s level). The sensor can be dispelled as if it were an active spell. Lead sheeting, force fields, and some exotic materials and magical protections block scrying effects; if that is the case, you can sense that the effect has been blocked.