How to use spike traps?

[nai249]

I linked them to a pressure plate but they just retracted and everyone just walked past them.

[Sinclair]

You either have to set the Pull lever job on repeat, or link the spikes to a pressure plate that is being constantly triggered. You can either put it in the middle of a high traffic area, or use water to depress it.

I've once built a repeating spike trap by having a bridge and a floodgate locking in a small pond of water with the pressure plate. Once the plate was triggered by water pressure it closed the bridge, opened the floodgate and let the water out automatically.