Land mine
Land mines are small, passive defense systems that explode when enemies come near them. Land mines can be placed freely on the map, but must be manually placed by the player. They do enough damage to kill a Small Biter or Small Spitter outright, but will only injure larger enemies.
Land mines are the only passive defense in Factorio; if an alien is hit by a land mine, they will not start chasing the player. However, if a biter notices the player placing a land mine, they will quickly destroy it without causing an explosion.
By carefully placing land mines around the edges of encampments, the player can wipe out small groups of aliens without being targeted. They can also be placed around the walls of a base to provide an extra layer of temporary defense.