Hello,
SMS commands are the "classic" way to contact an Anti-Theft installation.
Send a message to the lost phone with a command like this:
2222 locate
(replace 2222 with own avast! PIN - it’s 4-6 digits, only numbers.)
On the target phone (where you send the command to) the SMS should be received and executed invisible from the user's eye.
All SMS commands, along with a short description how everything works is explained in our manual available at:
<http://files.avast.com/files/documentation/mobile-security-user-guide-en.pdf>
it's short and easy to understand.
Werner