Sensor networks are poised to impact society in fundamental ways analogous to the impact of the networked personal computers. The rapid development of small-scale sensors coupled with wireless ad hoc networking capability foreshadows a day when our physical surroundings will wake up with sensory data, assuming it does not drown in the data first. In this lecture, Professor Ghrist will describe a recent calculus for sensor network data, whose origins lie in the century-old theory of algebraic topology. Sums and simplices, holes and homologies, counting and calculus, all converge to a tool for helping the walls to wake up.