 The tests showed that the people sniffer responded randomly to ammonia indicators, making it a very subjective instrument.Despite this, the ability of the people sniffer to detect other effluents, such as smoke, helped it to remain a valuable tool during the Vietnam War.The Viet Cong (VC) and the North Vietnamese Army (NVA) were able to develop effective, low-tech countermeasures to the people sniffers.