This is the trigger many of us use here in BC. They are available from Gord's Supplies, Prince George BC, phone 250 962 7767. I make up my own. It makes a trigger that has to be pulled to release it. The bar that holds the trap set has to be cut off to be exactly the right length to release with just a light pull on the bait.
This system selectively positions the ermine or red squirrel for a strike right behind the head.
The bait holder is a tiny stainless nail and a hole is drilled to put it through the plastic. The plastic is the same as what is used in bread boards. A small eye screw is used to hold the trigger.
Many types of bait will work well. For me a small cube of beaver liver (1/2 ") with a couple of drops of aniseed oil. I cut the cube up, put them in a plastic dish with a lid, and add some aniseed. Use direct from the container as needed. Keep frozen. A peanut in the shell can be placed over the top of the liver for better attraction to red squirrels. You now have a deadly combination for ermine and red squirrels.
Here is a picture of the trigger set up.
Here is the trap set in a box.
Here is a box I have made with a removable chloroplast front door. It is easily slid up if an ermine or red squirrel is frozen in the hole.