Chill Strike Trap (4e Trap)
From D&D Wiki
A magical object taking up one square, such as a pillar with a purple orb mounted on it, which fires a bolt of frigid purple energy towards any creatures that get within Range (10 squares). Once the pillar is destroyed the orb will fall and crack, harmlessly shattering into worthless glass. Players can make an Knowlage Arcana Check, DC 15 to identify it when they see it.