The dual technology multi-criteria fire detector uses detection of smoke by scattering of infra-red within the optical chamber coupled with thermal enhancement of the optical sensitivity, as well as providing temperature detection equivalent to grade A2. The smoke and heat channels can be controlled independently for day/night operation with intelligent data being evaluated by the Protec Algo-Tec 6000 interactive programmable algorithms. These sensors react across the range of fire products from large visible particles from smouldering fires to open flaming fires producing very hot smaller particles and are therefore suitable for use in all smoke detection applications. The environmental conditioning algorithms can be selected to filter unwanted alarms and enhance performance.