Clap (once, twice, three times ...) if you can hear me

This is a resource our teacher uses in order to have silence when her 4th year university students behave like primary school children.

How does it work:

When there is too much noise and chitchat in your class you say:

-Clap once if you can hear me.

-Clap twice if you can hear me.

-Clap three times if you can hear me.

-Etc.

Usually after three or four times you will have every children's attention. 

I like it because it makes people who are not paying enough attention feel like they are actually missing something and focus back onto group activities. In addition, it has to be said that its character is proactive and does not imply any punishment or authoritarian behaviour. What do you think?