In mobile systems, the requirements on event detection are
fundamentally different to those in distributed systems. Composite
event detection must be driven not just by the time of
occurrence of an event, but also by its location of occurrence.
Hence, the theory of composite event detection, as applied
in traditional DEBS, needs to be reassessed. In this short
paper, we motivate the notion of spatio-temporal event detection
and propose the base operators of a spatio-temporal
event language.