Trip Mine (D20 Modern Equipment)
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When this is activated (a standard action), it is placed into a single 5ft square (it's location is revealed only to the GM and to the creature or character that placed it, although that creature or character can reveal it's location to others). If any object, creatures or characters move into that square, it explodes, causing all objects, creatures and characters within 10ft to take 6d10 damage (reflex save DC=10+character level+Dex Mod for half). It can also be shot at from a distance to cause it to explode as well.
A trip mine has a purchase DC of 40, with a restriction of Mil (+3), and weighs 5lbs.