This description of a seashell radio is a harsh criticism of both the technology and the isolation of modern life caused by it.
After Montag has his eye-opening encounter with Clarisse, he returns to the mind-numbingly dull life that he leads with his wife. The metaphor Bradbury uses to describe the seashell radio is a perfect example and symbol of this existence.
The little mosquito-delicate dancing hum in the air, the electrical murmur of a hidden wasp snug in its special pink warm nest. The music was almost loud enough so he could follow the tune. (Part I)
Bradbury compares the seashell radio (imagine it kind of like an iPod and headphones), to insect sounds with an electrical tinge. These are not pleasant sounds. A metaphor is a type of figurative language that makes a comparison. This metaphor compares the insects to the radio.
Notice that Mildred is completely isolated from Montag. The seashells, and some of the other technology that they have in Montag’s community, serve to keep people apart from one another. Their insistence on television and seashell radios instead of human interaction, and their complete absence of literature and liberal arts, means that there is no real connection between people. Montag feels no connection to his wife.
Montag does not need to turn on the light to know what his wife probably looks like as she listens to the radio.
[He] imagined [his] wife stretched on the bed, uncovered and cold, like a body displayed on the lid of a tomb, her eyes fixed to the ceiling by invisible threads of steel, immovable. (Part I)
It is a mimicry of life, rather than life itself. The connection between people lost, people’s lives are empty. This is why suicide is so common. The imagery and symbolism of the tomb foreshadows Mildred’s fate, and the fate of a society that does not acknowledge its lack of consciousness.