Why does Apple 5s ring the SMS ringtone from time to time, but the screen is not bright and there is no message when it is unlocked?

If you check all social software and so on, and there are no unread messages, there are three possibilities:

1. The message is delayed, the voice has arrived, the message hasn't arrived yet, the mobile phone has no response, and the message will arrive soon.

2. The mobile phone is in an unclosed chat interface, with messages, sounds and unread prompts.

There is something wrong with the mobile phone. It may be poisoned or broken.

Note that if it is an Apple mobile phone, there is another situation. You receive a short message and only see it reminding you that you didn't click to read. The mobile phone will remind you again.