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Yeah, I was wondering the same thing. Not trying to start a war here but if you have that much concern about the places you're camping maybe the solution is to camp somewhere else?
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You stated that this was for "stealth" camping: Having an alarm is about as far away from being "stealthy" as it's possible to get. In fact, I would imagine that having such a system would only draw MORE negative attention to you.
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Have you had some bad experience while camping that you would feel comfortable sharing? The "sketchiest" place I've ever stealth-camped was in the parking lot of the Wal Mart in Gallup, NM. I've "camped" there 3 times in 3 different vehicles. If you know Gallup, you know it doesn't have the greatest reputation and yet - I've never had an issue camping there. One time I had the dog with me and she slept peacefully right beside me (well, until she woke me up to go pee at 4am!) The rest of the times I was by myself. Nobody bothered me.