Pre-programmed with 100,000 robocall numbers already blocked Additional number blocking capacity: 10,000 Press the Red Block Now Button or #2 from any cordless phone to instantly block robocalls, scam calls, political calls and telemarketers Optional feature to block international, private, unavailable or unknown callers plus entire area codes No mains power supply required ( uses the power from your phone line which is free) Compatible with all US landlines and home phones 3 years manufacturers warranty and lifetime technical support Caller ID services from your network provider is required for this product to function.