On a dusty road in northern Pakistan, a nondescript vehicle rounds a corner. Fifty metres overhead, a tiny drone buzzes unseen, spraying a fine mist across the vehicle's roof as it passes below. The vehicle is now tagged, and can be tracked from many kilometres away by an infrared scanner on a larger drone. This scenario may soon be played out now that Voxtel, a firm in Beaverton, Oregon, has won a US Air Force contract to develop a drone-based tagging system. Voxtel makes tagging materials -taggants - that can be used to discreetly label vehicles carrying smuggled goods, or people who are involved in civil disobedience or attempting to cross international borders illegally.
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