NO!!!! Do NOT do this. Even if the outside temperature is only in the 80s, a car gets TOO HOT to be safe for any living being. And, heaven forbid, the temps are in the 100s like they are here, a parked car is a death trap!
Who's car doesn't have an air conditioner?
Surely the car could be parked in the shade, tajen to the park, whatever.
Benjamen, my cat, was quite tge escape artist, and did not like to be picked up or held.
He also was large, strong, and had a full set of razor sharp claws.
(He sent the neighbor's Chow to the vet for stiches, lmao.)
He was ferel when I got him, so he did what he wanted.
Kitty wanted out, you let him out.
Anyway, why not cover the stupid alarm with something to muffle it?
It will still be obvious whether or not it is working.
Either it works or it doesn't- there is no need to blast the damn thing for hours.
Even then, there will most likely be frequencies that hunans cannot hear that your cat can, and these could be excruciating at worst, and disturbing at best.
It is unlikely, but there could be lasting effects that we cannot predict.
How big is kitty?
Welding gloves go up to the elbows with thick rawhide leather, and were great for when the vet had to examine Benjamen.
Although he was usually gentile with us, he was a real handful if you had to make him do anything.
Luckily, he was great with verbal commands, would walk with us and come when his name was called.
A nice set of welding gloves can be had for less than $10 and are a great investment anyway.
Take kitty for a ride with someone else, and enjoy the day.
You will have no enjoyment at home, even if the alarm gets muffled anyway.
In my dad's house, the dolts that put the fire alarms in put them in the wrong places (one is right in the kitchen!) and they tend to go off for un-fire events.
Once, an alarm went off in the middle of the night when I was not home, and Benjamen went from room to room and woke everyone up one at a time.
Never figured out if he knew that the alarm meant something was wrong, or (more likely) that it was annoying him and he wanted someone to make it stop, lol.
Just one of the many stories that endeared that cat to all of us.
(He is my avatar, btw.)