Spike Trap is a Devices Demon Hunter skill unlocked at Level 17. It is sphere thrown onto the ground that, when triggered by movement, erupts into a whirling device of spinning blades that damage to any target in contact. The damage is dealt steadily over time, so keeping an enemy atop the blades, via stun or positioning, will greatly increase the damage taken.
The Demon Hunter throws a sphere onto the ground that, when walked over, springs up into a whorl of blades and shadow, cutting any enemies in the vicinity.
 Skill Rune Effects
See the Spike Trap rune effects page for a more thorough description of rune effects, or any of the individual rune pages for numbers, screenshots, blue quotes, and much more.
 Skill Design
The skill works similarly to those found in the Assassin's set in Diablo II. It is a trap that, when thrown onto the ground, can be triggered by enemies who walk over or near it. It is best used in tight quarters to help control or "herd" the movement of the enemy. Much like the Wizard's Hydra, you can only have a set number of traps active at any time.
The following Demon Hunter passives provide a benefit to Spike Trap, runed or not:
Spike Trap was first shown at BlizzCon 2010 as one of the originals when the Demon Hunter was unveiled. Wyatt Cheng had this to say about it:
One of her themes is going to be traps and gadgets. This is not unlike some of the Assassin gameplay you might have seen in Diablo 2. In this case we want to sell again the shadow theme and the gadgets theme. We just take an ordinary trap spell, weave in some Shadow themes and the art kind of brings out the flavour, differentiates her from the other characters. Another thing I really like about Spike Trap is it has that sense of preparation. We want the player to know that the Demon Hunter is somebody that goes to sleep at night and dreams about killing demons. She wakes up in the middle of the night and goes "Oh, I have this great idea for a trap that will be awesome for killing demons", goes back to sleep, wakes up and kills a lot of demons. That's her thing.
Skill tiers were removed shortly before the beta started in September 2011, and Spike Trap became a level 14 skill, but was soon changed to level 16. The skill system was once again overhauled for the Beta Patch 13, and Spike Trap was classified as a Devices skill and moved to level 17.
Spike Trap can be seen in action on video here:
You can find pictures in the Diablo III screenshot and picture gallery:
The spike trap after activation.
That can't feel very nice.