My Havahart 1020 live mousetrap never fails to catch a mouse. After watching way too much mouse-cam video of mice romping in our crawlspace, the mice have absolutely no hesitation in entering the Havahart trap, and they almost never come back out without having set off the trap. But my lord, is it finicky to set. And if you've had any caffeine, forget about it.

What I wanted to replicate with this trap was the open, thru-tunnel design that the mice would feel comfortable entering, but that was easy to bait and set. This trap has no doors to push open, no ramps to climb, no small holes to squeeze through, and no closed chambers to enter. (Mice use echolocation and can tell if they've entered a dead-end, even when it is pitch black.) The rubber-band triggered doors at either end lay open until the mouse presses on either of the bait-bars in the center of the trap. The slightest pressure on the bait-bar tilts the doors up slightly past their tipping point and they both slam shut. (The 6th photo shows the trap innards in the “armed” position, the 7th photo shows the trap triggered.)

The trap also breaks into two identical halves with a simple clip to hold them together. This allows you to easily apply a little peanut butter to the bait-bars in the center and makes it much easier to clean out all the mouse poop after you've caught a mouse. It also makes it easy to release your captive: just place the trap on the ground, remove the clip, and then tip out the two halves. No having to lift the doors and have a panicked mouse run across your hand.

And lastly, this trap has several minor features that help prevent the trap from being prematurely triggered while the mice are either outside or inside the trap.

UPDATE: I've added a little vertical baffle to the end of the bait bar. This forces the mouse to climb up over the baffle to get at the bait, thus ensuring it puts its body weight on the bait bar. (Last night I caught a mouse just standing there gently licking off the peanut butter without triggering the door.)

Printing
All pieces were printed in PLA with 0.2mm layers, no supports. Print 2 each of the shell, door and bait bar, and one clip. The clip has built-in supports covering the dovetail grooves on either side – remove these supports after printing.

Assembly
In addition to the 3D printed parts, you will need four size 14 rubber bands (these are the ones used for bundling green onions in the produce section), and four 15mm long sections of 1.75mm filament to act as hinge pins.

As shown in the last photo, insert one of the hinge pins through the side of the shell, through one leg of the bait bar, and then into the door. The hinge pin hole in the door is tapered, so if you press firmly on the end the pin, it will stay put. Push a second pin into the other side of the shell. Check to make sure that the door can open and close all the way, and that pushing down on the bait bar will cause the door to lift up slightly. At this point, cut the protruding ends of the hinge pins flush with the side of the shell. Repeat for the second shell.

Take one of your rubber bands and loop it over nub at the top of the door and loop the other end over the nub at the far end of the shell as shown in the 8th photo. Repeat for the other side, and for the second shell. Push each door down flat and is should hold its position. Tapping on the bait bar in the center of the trap should trip the trap and send the door slamming shut.

Finally, the two haves can be clamped together using the clip piece.

Using the Trap
Remove the clip to separate the two halves. Tip up both doors in the closed position. Smear a little dab of peanut butter on the end of both bait bars (see 4th photo). Place the two halves on a flat surface and insert the clip to lock the halves together. Place the trap on the ground parallel to a wall where you suspect the mice will travel. Simultaneously, flip both doors down to the open position. Aim your mouse-cam at the trap, if you have one.

You can easily tell from a distance that the trap has been triggered if the rubber bands on the side are angled in an upward 'v'. Drive the trap and its captive at least 2 miles (!!! - that's right - that's how far they can travel to get back home) to a wild area or near the home of someone you don't like. Place the trap on the ground, remove the clip and tip out the two halves. Oh, and keep your car doors closed - the mice will make a bee-line for your car if given half a chance.