Non-profit organization Rainforest Connection hopes to use smartphones hung from trees to stop illegal logging. Using a specially designed app, old android phones can detect the sound of chainsaws. Upon hearing a chainsaw the phone can send an alarm to local forest rangers.
In order to stay on perpetually, the phones have solar panels attached to them. The power goes to helping the microphone listen for chainsaws within a 500 meter range. If the phone detects logging, it can send off a message to rangers with the location of the tree poaching.
Currently, the organization is also working to release a smartphone app so that anybody can get alerts. The app will let everybody get the same data that rangers are getting.