SMS has seen how to set unread.

After reading the message, you can't set it as unread. Repeated reminder of unread short messages means that when there are unread short messages on the mobile phone, it can be set to make the mobile phone repeatedly ring the prompt tone within a specified time interval to avoid missing important information.

Short message: ShortMessageService, referred to as short message service, refers to the text or digital information directly sent or received by users through mobile phones or other telecommunication terminals. The number of characters that users can send and receive SMS at a time is 160 English or numeric characters or 70 Chinese characters. On April 8, 2020, China Telecom, China Mobile and China Unicom jointly issued the White Paper on 5G SMS, which made the basic SMS service in China enter a comprehensive upgrade channel, and the traditional SMS will be gradually replaced by 5G SMS (RCS service).

The inventor of mobile phone short message is Finnish. Because Nordic people are sensitive and don't like to express by phone, they invented short message on a whim. Some people on the Internet say that the inventor of SMS is Marty Cooper, an American who works for Motorola, but he invented the mobile phone, not SMS.