>A quick and cheap tripwire pitfall trap.
1 redstone torch
2 sticky pistons
2 tripwire hooks
2 string (but you get 1 back, therefore only 1 string)
23 solid blocks (only counted blocks needed for this trap to work)
4x8x5 in size.
Original design: http://www.youtube.com/watch?v=fac4WlcSS74
This is a more compact version of the design above, thanks to jerryinyt for making a video about this trap.
This design was made in 12w23b.