Via Digg, a way-too-brief blurb on the development of genetically modified plants that can detect landmines. The company Aresa Biodection says plants would "change colour from green to red when growing nearby specific compounds. Hence, detection of various compounds in the environment is possible without using sophisticated detection methods and devices."
Update: Regine sends a link that better explains the plant, Thale Cress (Arabidopsis thaliana), and includes pictures of its color change. As Gizmag writes, Thale Cress makes its color change within 3 to 5 weeks of planting and can be used to detect not only landmines (of which there are around 100 million in the ground and active today), but unexploded ordnances and heavy metals in polluted soil.