The Oldest Trick (5e Trap)
From D&D Wiki
If the players loot a chest 1 of 5 things happen and all can be detected.
1 A giant ball falls from a hidden compartment,run or dodge it.(smashed player)
2 It activates the explosives (1d10 to everyone near).
3 Sand,or whatever sufocates them,drops from the ceiling.(hidden lever can stop the event)
4 Poison arrows trought the walls. (1d6+3 venom)
5 The room starts to shake and everything falls into a black pit underneath the room.(run)