Wireless sensor networks (WSN) are envisioned to fulfill complex monitoring 
tasks in the near future. A typical WSN application like object tracking fuses 
sensor readings produced by nodes throughout the network to obtain a 
high-level sensing result such as the current speed of a tracked vehicle. In 
order to produce correct results, the application typically has to process 
sensor events in the order of their occurrence at the sensor nodes. Temporal 
message ordering ensures that sensor events arrive at the application in this 
order. Due to the requirements and characteristics of sensor networks, 
temporal message ordering is a non-trivial problem in this environment. We 
motivate the need for temporal message ordering in WSN and present an energy 
efficient temporal message ordering scheme for sensor networks.