We present SpiderVision, a wearable device that extends the human field of view to augment a user's awareness of things happening behind one's back. SpiderVision leverages a front and back camera to enable users to focus on the front view while employing intelligent interface techniques to cue the user about activity in the back view. The extended back view is only blended in when the scene captured by the back camera is analyzed to be dynamically changing, e.g. due to object movement. We explore factors that affect the blended extension, such as view abstraction and blending area. We contribute results of a user study that explore 1) whether users can perceive the extended field of view effectively, and 2) whether the extended field of view is considered a distraction. Quantitative analysis of the users' performance and qualitative observations of how users perceive the visual augmentation are described.