In general, wireless sensor networks composed of many nodes which are located in ad. hoc environment and send the gathered data to sink node support only one way traffic. In those cases, it is not possible to send commands to nodes to react for exceptional events because the networks can not deliver downward data and the nodes run in pre-assigned fixed schedule. This paper expands the WSLP to bidirectional WSLP and implements a fire monitoring system on it, and shows the feasibility of bidirectional USN by demonstrating the usability of the process of reaction to a fire in the implemented fire monitoring system.