A Better Mouse (or Rat) Trap…Seriously

Setting rodent traps in awkward areas like attics and crawl spaces is hard enough, but checking traps in those locations every few days gets tiring, to the point where maybe you skip a few days, then forget where the traps are. Then you get, “What’s that smell?”.

I want to be able to check traps frequently, but without crawling around, preferably from a comfortable chair while using my my smartphone. There are products on the market that feature remote monitoring, but they are extraordinarily expensive, and often only available through professional exterminators. Victor also sells a WiFi enabled rat zapper, but my experience with it was not good. At $60, the price is not out of line for a WiFi enabled device, but it didn’t actually catch any rats for me.

I’ve always had decent results with basic snap traps with the yellow paddle, as shown below. I find these easier to set than traps with the tiny metal catch. The perfect solution for remote monitoring would be this kind of trap, but with a wireless status flag. In todays world of IOT devices, I’m a bit surprised that this isn’t already sold at Home Depot, but AFAICT, it’s not.

Low tech, but effective, snap trap

It seemed that the simplest and cheapest way forward was to piggyback on existing wireless door/window sensor technology. I chose Zigbee sensors made by ThirdReality because they were fairly cheap ($15) and used normal AAA batteries.


You could alternatively use Z-Wave or WiFi sensors. With either Z-wave or Zigbee sensors, you will also need some type of home automation hub. I already had a SmartThings hub set up for some lights, which included a Zigbee radio, and was able to connect my sensors to that.

Next was to devise a mechanism that would turn a trap snap into sensor motion, to either move the sensor near, or away from, the magnet, and do this without impeding the speed of the snap. I couldn’t think of a good way to do this with naked traps, but with the trap installed in a box, the problem became much easier. I had been meaning to make boxes anyway, because they would keep our dogs from messing with the traps.

The box contains a standard snap rat trap and Zigbee door sensor. When the trap triggers, the sensor falls way from the magnet, and sends a “door open” flag to the SmartThings app on my phone.

Boxes were made from plywood scraps I had around, but of course anything will work. One comment I’ll make about the box design is to make sure you can comfortably set the trap when it’s screwed down to the bottom of the box. My first box idea, with fixed walls on both sides, failed at this, it was too hard to work in the restricted space. In revision 2, shown here, one side lifts off with the top for easy access.

The sensor is connected to a stiff wire arm that is held under the snap bar when the trap is set. The arm pivots in a small notch filed in the top of the left box wall. When the top is in place, it holds the wire in the pivot slot. With the trap set, the end of the wire is held under the snap bar (see middle picture above). When bar snaps, the wire is released, and gravity pulls the Zigbee sensor away from the magnet, which is screwed to the side of the box. The sensor’s use of two AAA cells provides enough weight to break loose from the magnet.

The wire is bent as shown in the following pictures and is clamped to the sensor with 4-40 screws that thread into a small tapped piece of 0.5″x1.25″x0.125 aluminum. Under the aluminum plate, the rod is bent in a long U shape to surround the screws and prevent the sensor from sliding off or rotating on the rod.

I placed the completed box in a spot were I had seen rodent droppings. The following morning the SmartThings phone app told me that the “Rat 1” sensor had opened at 4:10AM the previous night. Sure enough, there was a mouse in the trap. Success! Now to go build more.

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