OK, OK, I know there are some who don't worry about such things or say they'll use their remote to set off their car alarm but I wanted a simple alarm for 3 specific situations based largely on the fact that any punk walking by with a screwdriver in his pocket ready to punch the lock in a mini van so he could use it for his B&E could also pop open the not really secure trailer door.
First, I've had second thoughts in more a couple of mall parking lots leaving the trailer unattended; second, in remote areas where there aren't any watching eyes I always feel there's a bit of a risk leaving the trailer unattended and lastly, overnight in a remote area.
So I put together a simple system for about 10 bucks. Any prying on the door will trigger the alarm. I can adjust the duration. The magnetic switch fits very nicely into the space next to the rubber seal and can't be seen from the exterior.
I had 2 sirens on hand so I tried them out wearing hearing protection. Hmm, not as loud as I thought. So I pried up the ear cup a bit and it was like someone slapped me on the side of my head. My chest reverberated. Yup, that'll do I thought.
Works for me.