The MERMAID undersea seismographs automatically float to the surface to deliver their data.
Developed to help seismologists better image the workings of the planet, the MERMAID (Mobile Earthquake Recording in Marine Areas by Independent Divers) floats will hover at a depth of about a mile and travel about three miles each day. As they drift with the current, the MERMAID devices listen for the sound waves associated with an earthquake. When one is detected, the device will automatically increase its buoyancy and rise to the surface within 95 minutes, transmitting the data to a main station. The MERMAID can also be commanded to return below the surface and resume listening.