How to send a message to all the connected users in SAP?

How to send a message to all the connected users in SAP?

Type  SM02 in the command field and press enter.

The system message  screen will open , 

 

in that (above) screen  click  create  button,  create  system messages  popup will  open,

 Here you can type maximum 3 lines of messages,   also you can  fix the  expire, delete  date &  time(optional)