Critter Deterrent





Introduction: Critter Deterrent

Our neighborhood, like many in the states I imagine, is crawling with feral cats. For the most part, I don't mind them; they keep the pigeon population down, they don't cause a lot of damage or raise much ruckus. (I do wish they would quit reproducing, though) We managed to rescue a kitten recently and she is adapting well to her new, cushier life LOL

Unfortunately, there is one male that insists on marking our front door. Every. Freaking. Night. There are few smells in the world more pungent than that left by a territorial cat. My boyfriend was at the end of his rope and wanted to trap the cat to turn over to animal control - a solution that didn't sit well to me as I know that amounts to a death sentence. So, to the drawing board where I came up with my pressure switch triggered Sonic Critter Deterrent. It went off 4-5 times the first night, and we haven't seen or smelled the cat since.

Step 1: The Supplies

Door alarm (got mine at the local dollar store): $1.00
2 pieces of cardboard or box (I found this box that the post office left at the office last year to introduce their program, it is a size we never use): Free
Aluminum foil: Pennies
Weather stripping (this was left-over from fixing a laundry room door): Free if scrap, A buck or so if purchased

A small amount of wire will be needed, your soldering gun, some spray adhesive, a bit of copper or aluminum tape

Step 2: The Alarm

These intruder alarms work with a magnet switch - when the magnet is away from the alarm, it sounds. This is perfect for us as we want the alarm in an "always on" state. When I opened my alarm up, I found two wires to choose from. I didn't want to eliminate the on/off switch, since I thought it would be handy to turn off the alarm during the day (don't want to scare the postman ;-) ) so I didn't touch the wire on that side.

Instead, I snipped & stripped the other wire, then soldered a piece of scrap wire to each side in order to extend them. I ended up with two longish wires coming from the side of the alarm. I wrapped the connections in electrical tape to ensure they didn't touch and short the connect before my new switch.

Step 3: The Switch

For our pressure switch, we need two pieces of cardboard with foil glued on. In my search for scrap boxes to cut up, I found this priority mailing box the post office had given us as part of a promotion. We never used it as the size is not what we need - but it is perfect for this. It was *almost* springy enough on it's own, but the weight of my doormat was just enough to trigger the alarm.

I used spray glue to attach a piece of foil to the inside top & bottom, then put a length of the weather stripping along each side. The rubber stripping was narrow enough to not interfere in the operation of my pressure switch, but resilient enough to push the top and bottom apart as soon as there is no longer any weight on the box.

I then stripped the free ends of the wires I had previously soldered to the alarm, and taped the bare ends to the foil inside the box with aluminum tape, one on the top, one on the bottom. At this point, if you switch your alarm on and push your box together, you should hear a non-too-pleasing screech from the device. You are ready to deploy it to scare away things that go psssst in the night.

Step 4: The Finish & Options

Place your pressure switch inconspicuously wherever you need to scare away varmints, sit back and listen to them get the surprise of their life. No harm inflicted.

For around $2 total, and less than ten minutes time, one of my favorite creations - because it is simple, practical, cheap & effective.

This switch could easily be adapted to other uses:
It could trigger a doorbell or a camera
It could trigger a multitude of scary devices for Halloween (light up a pumpkin, make creaky noises, drop a hairy spider on their head....)
It could trigger many pleasant things for Christmas (play a medley of carols, drop some mistletoe, have a Santa that "Ho, Ho, Hos"
It could trigger a recording of big dogs barking, making burglars & solicitors both think twice :-)



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    15 Discussions

    Instead of flipping the switch every day, you could consider a photo resistor and possibly a transistor, if needed, to let the sun activate and deactivate the power.

    2 replies


    This was a "quick & dirty" build so super basic. I think with a photo resistor, and perhaps even a solar charger, it would be even better.

    Personally, I would prefer a more discrete package and solar panels are a little bulky. If only they made decent rechargeable coin cells...replacing all of the devices in my house with NiCd rechargeables has already saved me about $100 and no more corrosion if they aren't taken out before storing electronics.

    A humane death is a better fate than the trials of a domestic animal without a home. They face animal abusers, wildlife, cars, poison, frost bite, I could go on and on.

    Believe it or not (to turn a phrase) I live in Mexico and we don't have a problem with feral cats (I hesitate to speculate why exactly) but I do have a problem with a neighbor's cat who comes around to "visit" my little "Baby", so any harsh control methods would be frowned upon.
    Your solution sounds like a perfect solution to my problem, and I'll give it a go.

    2 replies

    I don't know what part of Mexico your in. There is a feral dog problem in some parts. You probably know but they run in packs and they don't look anything like the dogs people keep as pets. I'm thinking that is the reason for not having feral cats. They probably kill them.

    Awesome - hope it works as well for you.
    (I did forget to turn it off one morning, so I had the pleasure of seeing a solicitor step on it & jump)

    Thanks for the patch :-)

    I'm really glad you found a way to just scare him off without hurting him. I'm a cat lover. I do agree that ferel cats are a problem. They need to be neutered. They spread diseases to house cats that are let outside. This is one reason mine don't go outside. The smell from a male cat spraying is hard to get rid of. Before I got my boy fixed he sprayed several of my dresses and jackets. White vinegar diluted with water will take care of the smell he left on the porch. I'd say 1 part vinegar to 4 parts water. For clothing a 1/2 cup of white vinegar in the wash gets the smell out.

    The best way to stop that smell is to just neuter the cat. Feral cats are an epidemic but only the community can get it under control. $20 feral cat sterilization at your local SPCA. A lot easier.

    I wish I could have caught him in the act - I imagine it was pretty comical - but he always came in the dead of night :-)

    Maybe I'll set up the camera and catch the next solicitors that come to the door LOL

    we also have boy cat scent problems. My wife found that although very stinky it is water soluble!So when our front steps or any other area gets the spray she uses my watering can and just goes around the porch at cats rear height and sprinkles it away. I will use your trick though on the neighbor brats that think 2am and 2pm are the same:)

    1 reply

    Indeed, we just got worn down cleaning up the door every morning - and of course our pets (2 dogs, 3 cats) found the smell fascinating

    I had trouble with neighborhood kids using my garage door as "base" for their game of tag while waiting for the school bus every morning. Since I worked nights, the banging as they slammed into it was quite unwanted at 7 a.m. No amount of pleading seemed to work. So, I started sleeping with my garage door opener and as soon as a kid touched base, I'd make the door *jump*. Scared the snot out of them and they started using the tree next door :-P

    Very good.

    I like your thinking!