Re-skinned pressure plates that only react to explosive force. Will immediately encase a 3x3x3 area in shock absorbent foam. My own use for these would be to have one in front of every machine that a creeper could get near. I'm tired of having to rebuild my stuff when ever someone on my server leaves my door open. Ban list is getting full... -.- Would also be nice to carry in your person for those times you just can't escape in time. Throw it down and pray. Of course, it wouldn't absorb ALL the impact, and a nuke going off would just blow through it, but TNT and creepers wouldn't be near the menaces.
Recipe:
Construction Foam
Stone (or iron/tin) Pressure Plate
Electronic Circuit