As the use of sensor networks expands, there will be multiple, independent networks operating in the same physical space. These networks will run heterogeneous applications and be managed by different entities. At the same time, the development of commercially available, general purpose sensor platforms makes it likely that co-located networks will be based on the same platform. Such networks will unavoidably interact with each other due their common communication hardware. "Semantic interference" occurs when frames transmitted in one sensor network are successfully decoded and (mis-)interpreted in another. This paper examines modes of conflict, co-existence, and cooperation that obtain in this context.