When the PIR sensor is activated, your MP3 files will play automatically (Note: They can usually be played on computers with Win7/XP, but not on computers with Win8/10). Perfect for shops: If someone enters the store, they will be greeted with a warm welcome. You can download different sound files depending on the application to get the desired effect. Practical anti-theft function: When you leave the house, the sound turns into a ringtone. The sound can attract and remind people who want to continue and deter thieves. Two power supply options: Comes with 3 AAA battery slots and a USB port, can be powered by 3 AAA batteries (not included) or the included USB port. (Note: Do not use USB instead of sound). The effective range of the infrared doorbell is 4 meters, and the sound plays when someone enters the effective detection area. Sound files can be replaced. Simply connect to your computer via a USB cable and copy the new sound files (MP3 format only).