Bird Gard Pro Plus Sonic Bird Repellent - 2 acres Repels birds on up to two acres. Vast array of sounds available in clear digital Change the chips on the fly depending on your needs AFTER PURCHASE we will contact you about which chip you need for the birds you want to repel, or you can contact us before or after purchase. The Pro Plus has two external speakers (you can choose to add up to four more) and two built in amplifiers for crystal clear, high volume digital sound.