Dear buyer:we produce wireless doorbell and home alarm system with high quality & very competitive price for 20 years in china; hope to find a way to cooperate with you. 1. Stylish modern design fits into any home and office. 2. 52 ringtones(16 chord)to choose from and 4 steps volume control(25~110db). 3. Simple to use and easy-to-install without the hassle of running any wires. 4. With up to 300m operating range in open space, 100m audible range. 5. Ip55/ip44 waterproof transmitter 6. Eye-catching backlight flashes when someone pushes the doorbell. 7. Different quantity of push unit(transmitter) and chime unit(receiver) are free to pair together. 8. If paired multiple push units in one system, the chime can be set to different for each push unit. 9. Using learning code to prevent interference from other wireless transmitters. 10. Easy to choose your change and select your favorite ringtone with forward and backward button. 11. Automatically save selected ringtone after power off. 12. Approved with ce, fcc, rohs certification.