Wireless sensor networks (WSNs) have attracted attention in recent years. Many sensors will be equipped in buildings and provide data about the context of buildings in the future. We can provide many kinds of services that use various context information acquired from wireless sensor networks. However, sensing programs may not be able to be executed concurrently on the same sensor node because of sensors? resource restrictions. So, sensing programs sometimes have to relocate to other sensors if necessary. In this paper, we suggest a middleware for the relocation of a sensing program. Considering severe resource restrictions in a wireless sensor network, we can make a sensing program with a small code footprint.