In this paper, we introduce the "Plug" sensor network, a ubiquitous networked sensing platform ideally suited to broad deployment in environments where people work and live. The backbone of the Plug sensor network is a set of 35 sensor-, radio-, and computation-enabled power strips distributed throughout the third oor of the MIT Media Lab. A single Plug device fulfills all the functional requirements of a normal power strip (i.e., four 120V, 60Hz electrical outlets; surge protector circuit; standard electrical connector to a US-style wall socket), and can be used without special training. Additionally, each Plug has a wide range of sensing modalities (e.g., sound, light, electrical current and voltage, vibration, motion, and temperature) for gathering data about how it is being used and its nearby environment. To our knowledge, the Plug sensor network is the first to embody the idea of designing sensor nodes to seamlessly become a part of their environment, rather than play the role of alien, if unobtrusive, observers. We argue this design principle is essential for sensor networks to succeed in the realm of ubiquitous computing.

Digital Manipulatives embed computation in familiar children's toys and provide means for children to design behavior. Some systems use "record and play" as a form of programming by demonstration that is intuitive and easy to learn. With others, children write symbolic programs with a GUI and download them into a toy, an approach that is conceptually extensible, but is inconsistent with the physicality of educational manipulatives. The challenge we address is to create a tangible interface that can retain the immediacy and emotional engagement of "record and play" and incorporate a mechanism for real time and direct modulation of behavior during program execution.We introduce the Backpacks, modular physical components that children can incorporate into robotic creations to modulate frequency, amplitude, phase and orientation of motion recordings. Using Backpacks, children can investigate basic kinematic principles that underly why their specific creations exhibit the specific behaviors they observe. We demonstrate that Backpacks make tangible some of the benefits of symbolic abstraction, and introduce sensors, feedback and behavior modulation to the record and play paradigm. Through our review of user studies with children ages 6-15, we argue that Backpacks extend the conceptual limits of record and play with an interface that is consistent with both the physicality of educational manipulatives and the local-global systems dynamics that are characteristic of complex robots.

Over the last three years we have built and experimented with the Pushpin computing wireless sensor network platform. The Pushpin platform is a tabletop multihop wireless sensor network testbed comprised of 100 nodes arbitrarily placed within a one-square-meter area. The Pushpin platform's concise form factor and extreme node density allow for fine-grained control of its environment and immediate user interaction, thereby uniquely situating it between simulated and real world sensor networks. This paper details our salient successes and lessons learned along the way. We also discuss how these experiences have shaped our vision of the future of wireless sensor networks and some concrete research directions to follow.