For a fairy to use a shield, he or she must increase their heart rate to such a speed that they vibrate too fast to be seen by most eyes. The ofiicially known ways to see through a shield are to use an anti-shield filter in an LEP helmet or Section 8 helmet. An exception is of Artemis Fowl II, who uses a camera that records at speeds of two thousand frames per second, and then freezes the image.
The downside to the shield is that it stops a fairy from thinking clearly and leaves a fairy unable to use fine motor skills (as stated in book 6). This side-effect can be counteracted by sucking the gut in and up. The movement gives fairies something to focus on, and makes the shakes less violent on the body.
Anyone looking at a fairy using the shield would see nothing except a faint shimmer, which is often mistaken for evaporation or a heat haze. The shimmer is only seen if a human is looking closely, which is rather rare. The tiny shimmer can be avoided by use of a Shimmer-Suit. The special suit vibrates with the fairy, averting the small giveaway of a shielded fairy. The Shimmer-Suit also captures any small amount of shielding magic and amplifies it, which makes "a small amount of magic go a long way".