"Headspace" (a term borrowed from the beat generation, where it connoted psychological privacy) is the technical term for the area surrounding an object or person in which their odour can be analysed. But odour detection is not limited to the discovery of drugs and explosives. Scientists and electronic nose entrepreneurs claim headspace analysis can reveal everything from the substances people have been in contact with and their emotional state, to their personal identity and ethnic origin. Although the science behind this field is nascent and the scientific validity of such claims is hotly disputed, they are gaining in stature. Researchers believe the unique smell that we each emit is tied to the makeup of the major histocompatibility complex, a group of genes found on the surface of T-cells that are crucial to the immune system. Several police dog handlers attribute their dogs' knack for identifying criminals to an ability to detect the scent of fear emitted by the guilty, and a synthesised version of this scent is available as a training aid.
— From Smells suspicious, a fascinating report on modern methods of olfactory surveillance. By columnist Amber Marks in the UK Guardian, with thanks to Gary Fredrick for the link.