Wireless Doorbell Intercom Rechargeable Smart Intercom Doorbells for Home Real Time 3 Volume Levels 1000m/3280ft Long Distance Electronic Doorbell for Home Power Supply Method: Rechargeable battery Working Temperature: -20 ° C to 55 ° C Transmission Distance: About 1000m/3280ft of open space, 20-50m/66-164ft of partition walls Working Frequency: B-gear frequency 462MHz, A-gear frequency 434MHz Working Hours: Charging the outdoor unit once takes about 8 months, while charging the indoor unit once takes about 3 days Charging Time: Approximately 5 hours when fully charged Music Ringtones: 38 ringtones Volume:  3 adjustment (standby machine volume adjustment key) Call Sound:  3 adjust call size (adjust volume key during call operation) Outdoor Unit Water Resistant Grade: IP54 Indoor Unit Water Resistant Grade: None Battery Capacity: 3.7V/1800mAh Product Colors: Black Product Quantity: 1 Outdoor Unit with 2 Indoor Units Outdoor and Indoor Unit Hosts Size: 116 * 56 * 18mm/4.6 * 2.2 * 0.8inch Water Resistant Cover Size: 121.5 * 61.5 * 31.3mm/4.8 * 2.4 * 1.3inch Charging Dock Size: 70 * 56 * 29mm/2.8 * 2.2 * 1.1inch