Given the price of metal detectors these days, I was suprised to see how easy it is to make your own. And you don't even need a smartphone for it - you only need some old stuff lying around, like a calculator, a transistor radio and an empty CD case (if you haven't cleared out the clutter yet). ...
You have a weekend house but there's no running water? You don't have a weekend house but are running in the jungle without any drinking water on you? Whichever the case, this will solve it for you. Here's a more sophisticated version that works the other way around: And here's the survivor version:
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