Which of the following devices is specifically designed to emit noise to repel birds?

The device specifically designed to emit noise to repel birds is the Screamer. This device produces auditory distress signals that can disrupt the environment for birds, making them feel threatened and encouraging them to leave the area. Screamers operate on the principle that loud, unpredictable noises can be a deterrent to birds, which are often sensitive to sound.

In contrast, porcupine wire is used primarily as a physical barrier to prevent animals from perching or roosting on ledges or structures; it does not emit noise and serves a different purpose. A live trap is designed for capturing and relocating wildlife, making it ineffective for repelling birds through sound. Camouflage netting is used to blend structures into their surroundings or to shield areas from wildlife visually rather than through sound deterrents. Thus, the Screamer is the most effective device for repelling birds by utilizing auditory signals.