LETTER: Sensitive smells

From Mr Christopher M. Rogers

Sir: There is a precedent for sensors that detect human smell ("Security sensors sniff out potential intruders", 15 January): the Americans dropped similar devices during the Vietnam war to detect guerrilla movements. Unfortunately for the Americans, the Viet Cong found that the detectors could be fooled simply by hanging containers of urine from the trees, and the scheme was not a success.

Let us hope the new devices do not suffer a similar fate, or it could make security guards' jobs even more unpleasant.

Yours faithfully,

Christopher M. Rogers

Edgware, Middlesex

15 January