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