We demonstrate a tool that allows inspection and debugging of deployed wireless sensor networks (WSN) by analyzing overheard radio messages. This tool can identify common problems such as node crashes, reboots, routing problems, and network partitions without instrumentation of sensor nodes. Existing approaches to identify performance problems and bugs in deployed WSN such as Sympathy [5] require to add logging and debugging code to the application running on the sensor nodes, with monitoring traffic being sent in-band with the sensor network data to the sink. These approaches result in significantly increased resource consumption in the WSN and bugs in the sensor network may also affect the monitoring mechanism. The presented tool is an implementation of our Sensor Network Inspection Framework (SNIF) [6], which consists of hardware to overhear network traffic, a data stream framework to decode and analyze overheard messages, and a graphical user interface to display the network topology and node states. We will first provide an overview of the hard- and software before the demo setup is presented. We also briefly dicuss closely related work.