This is the solution a California-based group Rainforest Connection has found to save our vulnerable forests.
Old Android smartphones are fixed in a waterproof casing, with a solar charger and mounted high in the tree canopy where they are hard to see.
Each device continuously captures all ambient sound, and can detect the sounds of destructive activities - such as logging/chainsaws - up to one kilometre in the distance.
When the phone picks up the sound of a chainsaw, gun shot, distress, the device transmits an alert to a cloud server which in turn sends an SMS message to first responders.
"The forest can speak - and you can hear it. They can hear the first saw, they can hear the rifle shots when people are shooting animals and shouldn't be. They can tell when the forest is under attack by people who are breaking the law," said Neil Young, the creator of the project.
Each phone can protect an area of 300 hectares of forest.
In the Kalaweit Supayang Nature Reserve in West Sumatra, Indonesia, the system has been in place for an year, and protected 135 hectare from illegal loggers, Scientific American reported.