If they complete their nest, they will lay eggs. Your deterrent measures should be done prior to the completion of the nest. In addition to the auditory and visual deterrents, you may also hose down the nests while they are under construction. To do so after the nest is built will only create heartache for you and the swallows. Keep in mind, we are suggesting deterrent measures, not methods of eradication of these birds.
Swallows consume enormous quantities of flying insects and are, in fact, an asset to our area.
The old 'scarecrow' isn't a bad idea when dealing with crows and ravens who invade our vegetable gardens and fruit orchards. With their keen senses of sight and hearing these birds can be deterred by an unfamiliar moving object or a portable radio placed in the garden. Adorn your garden with a unique scarecrow and hang a few pie tins from his arms for further effect. Crows and ravens are extremely intelligent and may get wise to your scarecrow. The secret is to keep them wondering.