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 :-)