The Sensor Internet at Work: Locating Everyday Items Using Mobile Phones Christian Frank, Philipp Bolliger, Friedemann Mattern, and Wolfgang Kellerer We present a system for monitoring and locating everyday items based on users' mobile phones that are augmented with the capability of detecting near-by objects which are electronically tagged. It includes different usage scenarios from storing the context in which an item has left the sensing range of the local device to allowing object owners to search for objects using the infrastructure of mobile phones carried by other users. Next to describing the design of our object monitoring system, we provide an algorithm which can be used to search for a lost or misplaced item efficiently. Furthermore, we demonstrate the practicability of such wide-area search by means of user-carried sensors in a series of simulations complemented by a real-world experiment.