Until fairly recently the detection of heatings was based on men seeing or smelling smoke and the laboratory analysis of mine air samples. Continuous monitoring of carbon monoxide by means of tube bundle systems has been a big step forward in detecting spontaneous combustion of coal and has found widespread acceptance in U.K. mines; general fire detection relies on shaft monitors. Both are based on infra-red analysers like the Unor CO-analysers that can be installed underground. In recent years British laboratories have developed and adapted several devices based on other principles: ionisation, semi-conductors, electro-chemical cells, thermistors, detection "thermal noise", infra-red imagers. All these instruments are briefly described by the authors in this paper presented by Mr. Makower.