Drone-dropped "dragon eggs" made to monitor volcanoes

As long as the volcano isn't about to erupt, each device remains dormant, consuming very little power – in fact, they're claimed to feature "the lowest stand-by power consumption in the world." Upon detecting even slight volcanic tremors, however, they wake up and begin sensing/recording temperature, humidity, vibrations, and the presence of various toxic gases. They can operate individually, or in a linked multi-egg network.