The ELK-100 Siren Driver is a great choice for residential and commercial security installations. It draws less current than most siren drivers, and offers two volume levels (example: one indoor, the other outdoor) simultaneously. Our exclusive MilliMiser™ option allows further reduction of current draw for controls that have limited alarm or auxiliary output power. The ELK-100 has two inputs, Yelp & Steady. The Steady sound overrides the Yelp.