Viking Door Entry Control for 4 Entry Phones, Provides CO Sharing, Call Waiting, and One Aux Contact Allows an entry phone to share a single telephone line with a residential or business telephone system House phones ring with C.O. line cadence or distinctive ring when the entry phone Call button is pressed Compatible with these Viking entry phones: - E-10, E-20A, E-30, E-40 Handsfree Phones - K-1500-7 Stainless Steel Panel Phone - Or use with any analog touch tone phone Provide entry phone activated chimes and whole house paging when used with Viking model SLP-1 Produces double Call Waiting tones One set of normally open and normally closed contacts available for operating a doorbell, camera, lights, etc. Add door strike capability with the Viking model RC-2A Remote Touch Tone Controller