What does it mean that the SMS alarm content is sent to the last 3 digits of 12 1 10+ area code?

Generally speaking, the area code has four digits. For example, 0825-8524-11indicates that the last three digits of the area code indicate 825 (that is, it is sent to 12 10828).

There is also a three-digit China area code with three digits: Beijing 0 10 Guangzhou 020 Shanghai 02 1 Tianjin 022 Chongqing 023 Shenyang 024 Nanjing 025 Wuhan 027 Chengdu 028 Xi 'an 029.