This is a simple smoke detector shown in the given circuit diagram. This can be used to give indication when smokes level is exceed to the allowed directed level. The circuit has single transistor T1 (NPN) and a galvanometer for indication. The transistor works as a switching amplifier here. It simply gets biased voltage through variable resistor give voltage to the meter which indication. To smoke chimney a sensing probe can be made from any insulated pipe. When smokes filled up to the top level and sensing probe gets active to an extent and goes reading at galvanometer. The length of probes can be extended unto 10-50 cm and it will not affect the performance of the dive in any way.