Sensor Doorbell - A sensor, a welcome chime, a dual-purpose doorbell. Sensor operating voltage: DC 3V (two 5-cell batteries, not included) Receiver operating voltage: DC 9V (one 9V battery, not included) Transmission frequency: 315MHZ Transmission distance: 100m (in an open, clear, and interference-free environment) Infrared detection distance: 3-7m Ringtone: classic monophonic (Towards Alice) Avoid installing the sensor in a position directly facing a large change in airflow and near heat sources (e.g., cold air outlet, fan outlet, electric stove, or near a heated area). Do not install the doorbell in direct sunlight or rain, or near metal objects. The sensor should be installed at a height of about 2 meters; side detection of the sensor is more sensitive than linear detection (the human body directly facing the sensor) and generally needs to be installed on the side or top of the front door and adjusted to the correct position using a mounting bracket for better detection results. The distance between the sensor and the receiver should be as large as possible to minimize obstacles and other interference with the wireless signal. Generally, the distance between the sensor and the receiver should be about 10 meters if there are walls obstructing it. If the doorbell appears to receive at too short a distance or malfunctions, check the sensor batteries or replace them. If the ambient temperature is too high (more than 30 degrees), the distance between the sensor and the receiver will be reduced, which is normal.