We have several window alarms similar to these
https://www.amazon.com/Wireless-Discreet-Security-Magnetic-Operated/dp/B013XJHM1Y/ref=sr_1_3?ie=UTF8&qid=1492031685&sr=8-3&keywords=battery+alarm+for+door
I bought several at Harbor Freight for a few bucks each and those suckers are loud!
Fasten one side on an inconspicuous place on a gear container or box other piece of camping gear you often leave at the campsite. Drill a small hole in the magnet container and tie on a small piece of fishing line or similar. OR, fasten the line to something small you can stick to the magnet adhesive. The line can be as long as need be. Tie the other end of the line to some fixed object like a table leg. I often drive a small tent spike into the ground and attach the loose end to it.
Along comes the potential thief. They pick up the protected object and (if you are stealthy with the location of the side attached to it) will never see the small line. Grab and go.
110 decibels of alarm go off.
Now, a determined thief would look things over carefully but grass, dirt, rocks other stuff in a campsite pretty well camouflages the alarm. Most theft of camping gear is opportunistic and impulsive and so is the thief.
I have never had a piece of equipment stolen. But I probably have just been lucky. How sad how camping has changed in the last several years. We mostly never gave this stuff a thought until a few years ago.
A friend rigged a mouse trap (the old small board with the big spring type) under the appropriate place on a camping table. His fingers sure were blue for a spell after he forgot to unarm it upon his return to his camp.
PSW
2013 Phoenix Cruiser 2350
2014 Jeep Cherokee behind it
and a 2007 Roadtrek 210P for touring