Clipped onto a rope, climbing high up in a tree swaying in gusts of wind, Topher White finally reaches the roof of the rainforest and opens a laptop to run checks on a machine he built to transmit 24-hour live sound from the surrounding forest.

The machine is one of 27 so-called Guardian sensors eavesdropping on forests in Indonesia's West Sumatra province, to listen for chainsaws as a way to tackle illegal logging in the region.

Over the next five or six years, White hopes to install tens of thousands of these audio sensors in forests around the world.