Feature:1. Frequency of Doorbell is in line with the national regulations, will not produce harmful electromagnetic interference.2. Battery take‑in and take‑out easily for outdoor machine, using 4pcs AAA batteries, and service life can up to four months, but the battery is not included.3. The indoor machine doesn't need batteries, and it is connected with USB data cable.4. Volume adjustable and ringtone changeable, the voice quality is clear and the speaker sound is loud.5. Installed easily, can straightly stick doorbell to the wall with adhesive tape and less time consuming.6. Using learning code to code, an outdoor machine support many indoor machines, non‑interference.Specification:Condition: Brand NewItem Type: Doorbell Color: As Picture ShownMaterial: ABS PlasticThe Outdoor MachineBattery Model: 4pcs AAA Batteries for Power Supply (Not Included)Working Temperature: -20-55℃Transmission Distance: Approx. 200m/218yd of Empty Place, 5-50m/16.4-164yd of Place with ObstaclesWorking Frequency: 467.6375MHZWorking Time: Four monthsWaterproof Rating: No Waterproof FunctionThe Indoor MachineVoltage Range: 5V 1AWorking Temperature: -20-55℃Transmission Distance: Approx. 200m/218yd of Empty Place, 5-50m/16.4-164yd of Place with ObstaclesWorking Frequency: 467.6375MHZWaterproof Rating: No Waterproof Function.Package List:1 x Indoor Machine1 x Outdoor Machine1 x Screwdriver1 x Discription2 x Adhesive TapeNote:The outdoor machine can be used with batteries for a long time. It is better to connect the indoor machine to the power supply.