Patent US 6,859,528

An accessory for association with a telephone answering machine, which blocks unwanted telephone calls. The “ringer” of the answering machine is de-activated: an incoming “ring” signal causes no “ring” sound. But the answering machine still answers, and may, or may not, say “Enter your password now.” In either case, the caller knows that a password is required, and enters it, using the keypad on the caller's telephone. The accessory “listens” to the password. If it is correct, the accessory actuates its own acoustic ringer, notifying the owner that a password-holder is calling. The owner, if present, may answer the call. If the password is incorrect, no “ring” sound is generated, but the caller may leave a message on the machine, as usual. Thus, only password-holders can cause a “ring” sound, but no callers are blocked from leaving messages.