OPERATION The state-OT-theeart: Doorbell Telephone Signaler will alert you when someones comes to visit or calls you on ihe telephone. The Doorbell/Telephone Signaler, Model DBO is the only doorbell and intercom signaler that requires no wires and can be installed in seconds. DB200 will alert you halt someone is at your door or on the telephone by flashing one or more lights around your home.