Even more so than water, frequencies can leak out of the tiniest of spaces. That said, you have to tightly roll down the bag at least 3x (5x is optimal), and secure the clips together. You will then notice the bag is air-proof as well as water- and signal-proof as well. To test its signal-blocking capabilities, simply drop a smart phone inside, roll up tightly as described above, and call it from another phone. When it does not ring, you’ll know it’s working. This is for the 5 liter, 10 liter and Backpack.
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