The infrared doorbell has 4 meters of effective sensing distance, and it play the prepared sound when someone enters the effective sensing range. The audio files can be replaced by yourself, just connect it to computer by USB data cable, then copy new audio files(MP3 formats only) to the player. Your MP3 files playback automatically after the PIR sensor has been activated.(Note: it can be recognized on Win7/XP computer, but it may be not recognized on Win 8/10 computer) Widely Use in Shop: When detecting the human body passing, it give out warm welcome, Greeting prompt, warnings prompt, playing voice advertisement or others. According to the different applications, different audio files can be downloaded to have suitable effect. Two Power Supply Ways: Equipped with 3 *AAA battery slots and Mini USB port, it can powered by 3 * AAA Batteries (not included) or the included Mini USB charge port. (Note: Do not support replace audio through Mini USB). Practical Anti-theft Function: When