The Smoke Pencil is an ingenious gadget for pinpointing air leaks and tracking down hard-to-find gaps – ideal for air leakage tests of new or existing houses. When the trigger is pressed, a plume of smoke-like substance is released. This is actually generated from a harmless glycerine-like fluid, giving off a slightly sweet smell. When the trigger is released, the “smoke” stops, making it highly controllable. The field kit comes with a fan contraption and two gauges of tip that can be attached for issuing a very fine flume of smoke for detecting the smallest of air leaks. There are six batteries for the Smoke Pencil and one for the fan. There is an 80ml bottle of fluid (enough for several hours’ worth of draught investigating), a screwdriver for the base so you can fit the batteries easily, and one more battery for the fan. These are all packed into a sturdy case for taking out and about with you.