Panasonic KX-TGA523M 5.8GHz Accessory Handset for KX-TG5200-Series Expandable Phones 5.8 GHz digital spread spectrum signal For Panasonic KX-TG5200M-series expandable phone systems Caller ID with call waiting, 50-call log AM/FM clock radio/alarm in base unit Light-up antenna signals new calls and messages Additional Base Model KX-TG5200 Series is required for this set to work, It will not work without it.