On some phones (all Nokias, some Siemens, Ericsson, Motorola etc..) a class 0 message will appear as a flash SMS message. These messages appear on the screen immediately upon arrival, without the need to press any buttons on the phone. If the data coding scheme is set to 16-bit unicode (ucs2), and the message starts with "0001", it will appear as a blinking flash message.
Octet Value Description TP-DCS 18 16 bits (UCS2), message class 0 TP-VP AA Validity period TP-UDL 0C User Data Length, 12 octets TP-UD 00 01 00 41 00 6C 00 65 00 72 00 74 User Data, message "Alert"
This table shows some relevant octets in a flash SMS message. The first unicode character ("00 01") enables the blinking. The maximum length of such a message will then be 69 unicode characters.