In a ubiquitous computing environment, small computers attached to physical objects are required to send sensor data to many other nodes on a narrowband wireless network to provide various types of context-aware services. To reduce the cost of sending sensor data, this paper proposes a notation to indicate a pair of objects to share data with each other, based on the 'contact' relation between objects. We call this notation, contact-based notation (CbN). In our method, because each node can send data only to nodes contacting the node physically based on the notation, we can reduce both the distance between nodes and the amount of nodes to which to send data. Moreover, this paper describes an experiment conducted to examine the communication costs on each sensor node described in our proposed notation. The results show that the cost of our method is lower than the cost of the simple broadcasting method.