Surveillance Magic is a type of magic used to see into the Duat, the magical realm underneath the mortal world. Using it, a magician can locate people even in the dark, gods, demons, godlings etc.
Carter used it to see Thoth and how many demons were attacking him, estimating the time Thoth had before he would be overwhelmed. When reinforced with power from gods, the magician can see further in the Duat and his/her senses are expanded greatly. This was used by Carter and Sadie Kane and briefly Percy Jackson while hosting Nekhbet.