Continued advances in information technologies are enabling a growing number of physical devices to be imbued with computing and communications capabilities. Aircraft, cars, household appliances, cellular telephones, and health monitoring devices all contain microprocessors that are being linked with other information processing devices. Such examples represent only the very beginning of what is possible. As microprocessors continue to shrink, wireless radios are also becoming more powerful and compact. As the cost of these and related technologies continues to decrease, computing and communications technologies will be embedded into everyday objects of all kinds to allow objects to sense and react to their changing environments. Networks comprising thousands or millions of sensors could.