Trees in Brazil are being fitted with a device which will call for help when they're cut down illegally.
A battery-powered tracker the size of a smart phone is hidden in the branches of a tree and automatically switches on when the tree is chopped down.
The device waits for a mobile signal, which it can pick up from 20 miles away and then calls for help.
When the authorities receive a call, they swoop in and arrest the illegal loggers.
The tracking device can be left in the trees for a year before needing new batteries.