The Xeno Siren is a useful satellite when needing to control or kill aliens. Peacefully, one can attract aliens using a Xeno Siren to a frigid zone on the map to prevent them focusing on your cities. You can also use them in conjunction with Ultrasonic Emitters and Nanohives to slowly kill them and morbidly gain Science. They can also be used as an obstacle for enemies should you need a crude barrier to slow down an opponent's army. Try to use them early on to assist alien control.