1. A modular general purpose sensor unit, comprising: a sensor array layer to receive and condition data from at least two different types of sensor; a general purpose intelligent processor and control layer to process at least said conditioned data and produce output data derived from said conditioned data, said processor and control layer including a reprogrammable memory for storing application specific software to control the operation of said processor and control layer, said output data being at least partially different from said conditioned data; a power layer for providing power to said sensor array layer and said processor and control layer; wherein said sensor array layer, said processor and control layer, and said power layer are layered to form a sensor module.