For this achievement you will need to destroy every monster that attacks you when the monsters break down the door to Zach's house. The game tell's you to use your special melee wepaon but don't. Only use the following traps. There are only 3 in the house.
Fire Place - To the right of the door where the monsters break in is a fire place that you can lure the monsters into and light them on fire until they die.
Lawn Mower - In the backyard of the house is a lawn mover that you can activate by pushing
and letting it run over the monsters. (recommended trap)
Falling Objects - There will be objects that come loose and hit the monsters, lure them over these falling traps.