Difference image (DI) monitoring is proposed as a new way of operation of low-cost CMOS cameras.

DI monitoring (DIM) allows optical changes in a scene to be compressed into a single time-dependent analogue output signal.

DIM signals can be merged with scalar output signals of other orthogonal sensors to form heterogeneous sensor arrays.

DIM cameras and metal oxide (MOX) gas sensors have been merged into heterogeneous sensor arrays to form innovative fire detection systems.

The performance of heterogeneous DIM/MOX sensor arrays has been positively assessed in typical fire detection scenarios.