What is "tripflare"

A tripflare is a device used by military forces to secure an area and to guard against infiltration. It consists of tripwire around the area, linked to one or more flares. When the tripwire is triggered, as by someone unsuspectingly disturbing it, the flare is activated and begins burning. The light from the flare simultaneously warns that the perimeter may have been breached and also gives light for investigating. In defensive operations, trip flares are usually placed in predetermined kill zones with machine guns sighted on them.