Mobile phones could become the largest surveillance system on the planet. These ubiquitous, networked devices can currently sense and upload data such as images, sound, location, and motion using on-board cameras, microphones, GPS, and accelerometers. And they can be triggered and controlled by billions of individuals around the world. But the emergent, wide-scale sensing systems that phones support pose a number of questions. Who will control the necessary infrastructure for data storage, analysis, sharing, and retention? And to what purposes will such systems be deployed? This paper explores whether these questions can be answered in ways that promote empowering surveillance: large-scale data collection used by individuals and communities to improve their quality of life and increase their power relative to corporations and governments. Researchers in academic and industry laboratories around the world are currently coordinating mobile phone networks for purposes that expand the definition of surveillance. Technology movements, variously called personal sensing, urban sensing or participatory sensing, have emerged within the areas of social computing and urban computing. These research programs endeavor to make ubiquitous devices such as phones a platform for coordinated investigation of human activity. Researchers are exploring ways to introduce these technologies into the public realm, a move that anticipates sensing by people across the world. This paper uses ethnographic data collected in a sensing development laboratory to illuminate possibilities that participatory sensing holds for equitable use, meaningful community participation, and empowerment. Analyzing the motivations and values embedded within the design process and resulting technologies reveals ways in which participatory sensing builds tools for empowering surveillance and responds to the many ethical challenges these new technologies raise.