This article examines the various types of technology used in modern buildings, tunnels, vehicles etc. to detect unwanted and potentially life-threatening fires. In selecting a detection system there is a need to balance responsiveness, reliability, cost and the potential for false alarms (sometimes referred to as ‘nuisance activations’) and no one type of system provides an optimum solution. The detection of fires involves a whole range of fundamental scientific principles as well as the application of advanced technological developments.