Old phones are listening.

Wall Street Journal has an interesting piece on how old smart phones are being used to listen for disrupted sleep patterns, illegal loggers, gunshots, breeding cicadas and a host of other sounds:

App makers have long focused on detecting speech and music, but some upstarts are turning to a wider variety of sound-detection tasks. They are taking advantage of more sophisticated mobile hardware and software to recognize distinct audio patterns.

In one of the quirkier ideas around sound detection, a company called Rainforest Connection wants to mount smartphones in trees to detect chainsaw noise and quickly notify local authorities about illegal logging. The company, founded last year, has launched a $100,000 Kickstarter crowdfunding campaign and partnered with the Zoological Society of London to kick off the project in Cameroon.

“It will be a trend in the near future,” said Tauhidur Rahman, co-creator of BodyBeat, a wearable smartphone project developed at Cornell University.

A crude prototype of BodyBeat, revealed in mid-June, uses an external custom-made microphone to track body sounds, such as breath or cough, with the ambitious aim to detect illnesses or record food consumption.

The microphone is placed on the neck with a 3D-printed neckpiece, which is plugged into a small audio processing device that is wirelessly connected to a smartphone. BodyBeat authors plan to redesign the system for better usability in commercial applications.

“Privacy is critical both to adoption and to the public’s perception of all of these technologies,” said James Bedlock, a senior vice president of ShotSpotter, a company with about 6,000 custom-made sensors deployed nationwide to detect gunshots. These sensors use the hardware similar to cellphones.

He adds that these apps are not generally streaming audio anywhere, but instead are exchanging small portions of sound-describing data, with the processing systems sitting in the cloud.