Features: 1. secure automatic answering of cell phone calls. 2. 1200m Bluetooth communication distance between the five intercom lines. 3. support mp3 / GPS / cell phones. 4. eight hours of talk time. 5. automatic pairing link with cell phones with NFC function. Specifications: Bluetooth version: 5.1 Remote control distance: 10M Chip: CSR BC5 Battery capacity: 550 Battery type: Polymer Charge and discharge times: 500 Operating voltage: 3.3V-4.2V Talking time: 8 hours Standby time: 120H Charging time: 2.5H Radio frequency band: FM87.5~108MHz Speaker power: 0.25W Operating temperature range: -10 to +45 Charger specification: DC 5V 1000mA