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LANDMINES lurking in former combat zones could be uncovered just by listening for them.

A major obstacle to clearing mines in poorer countries is the cost. In one method, mine clearers beam a low-frequency sound wave into the ground – which gently vibrates any buried mines – along with a radar beam. When the radar beam bounces off any vibrating mines it is reflected back at a different frequency. The problem is that radar sensors cost hundreds of dollars.

Now Gregg Larson and James Martin at the Georgia Institute of Technology in Atlanta have shown that these vibrations can also be detected using $65 microphones poised 1 centimetre above the ground (). The technique could slash the cost of clearing mines, they say.