From NASA JPL via geology.com:

PASADENA, Calif. — Scientists have placed high-tech “spiders” inside and around the mouth of Mount St. Helens, one of the most active volcanoes in the United States. Networks such as these could one day be
used to respond rapidly to an impending eruption.

On July 14, 2009, these spider pods were lowered by cable from a helicopter hovering about 100 feet up (30 meters) and gently put in hot spots inside and around the volcano crater…