A Proximity flare was a type of early warning system.[1]
Characteristics
Used by soldiers and scouts as early warning systems for camp perimeters, a proximity flare was a flare launcher consisting of a small tube with a spike on the bottom, allowing it to be securely placed in the ground. Sensors inside the tube could detect nearby shifts in air-pressure; when an object of sufficient size passed within ten meters of the launcher, it would fire the flare into the air and illuminate the area.[1]