People sniffer

The detection method used by people sniffers depended on chemical compounds that are emitted only by human beings,[1] such as those found in urine and sweat.

[4] In 1967 the Army Scientific Advisory Panel sent John D. Baldeschwieler to Vietnam in order to conduct controlled experiments and determine the ability of the people sniffers to detect ammonia.

[1] The Viet Cong (VC) and the North Vietnamese Army (NVA) developed effective, low-tech countermeasures to the people sniffers.

(Snoopy's ability to detect smoke meant it could easily locate ground troops firing with small arms, even if under cover and camouflaged.)

[1][5] Tactics such as these essentially rendered people sniffers ineffective in jungle terrain, but they remained useful in open areas, such as those found in the Mekong Delta.