For many people, smartphones serve as a technical interface to the modern world. These smart devices have embedded on-board sensors, such as accelerometers, gyroscopes, GPS sensors, and cameras, which can be used to develop new mobile applications. However, the sensors also pose privacy risks to users. This work describes BlurSense, a tool that provides secure and customizable access to all of the sensors on smartphones, tablets, and similar end user devices. The current access control to the smartphone resources, such as sensor data, is static and coarse-grained. BlurSense is a dynamic, fine-grained, flexible access control mechanism, acting as a line of defense that allows users to define and add privacy filters. As a result, the user can expose filtered sensor data to untrusted apps, and researchers can collect data in a way that safeguards users' privacy.