Resources Gun

An intruder is someone that is not supposed to be there (usually disguised as visitor, also can be disguised as a colonist), and starts killing colonists as soon as they have entered an airlock. A way to stop that is having Guards, or placing the colony in Red Alert so that colonists will also attack (not wise if they are unarmed). One way to prevent casualties is to keep control centers and sick bays near airlocks to heal your colonists.