2 Way Voice Intercom System Wireless Electronic Doorbell Intercomunicador for Patients Item Type: 2 Way Voice Intercom System Material: ABS Battery: Inner Machine: Polymer Lithium Battery 3.7V 1800mAh x 1 (Included) Outer Machine: Polymer Lithium Battery 3.7V 1800mAh x 1 (Included) Battery Power Supply: DC5V/1A Operating Temperature: -20°C-55°C Transmission Distance: Approx. 1000m / 3280.84ft in open space, 20-100m / 65.6-328.1ft through walls, 1-8 floors Working Frequency: 410-490MHz Working Time: Approx. 3 days on a single charge Charging Time: Approx. 5 hours to fully charge Music Ringtones: 38 Melodies Ringtone Volume: 3 Levels Sdjustable (Volume Adjustment Key in Standby Mode) Call Sound: 3 Levels Adjustable for Call Volume (Volume Adjustment Key During Calls) Size: Main Machine of Doorphone and Indoor Intercom: Approx. 116 x 56 x 18mm / 4.57 x 2.2 x 0.71in Waterproof Cover Size: Approx. 121.5 x 61.5 x 31.3mm / 4.78 x 2.42 x 1.23in Charging Dock Size: Approx. 70 x 56 x 29mm / 2.76 x 2.2 x 1.14in