Classroom Quiet Signal

I like the idea of a classroom quiet signal.  I teach science and that means hands-on labs and group activities.  It can get kind of loud sometimes!  I do not like the idea of yelling, which is just far too draining to me.  I think my students in middle school would like it if I did yell for quiet because I would probably look funny doing it! My idea this year is to use some sort of signal that I will teach them in the first week of school.  I have heard many ideas from the primary teachers who use these every year but not too many from middle school.  The best ones I have read about lately are using a rain-stick or a wireless doorbell purchased from Home Depot as the signal.  The doorbell would be quite funny the first time you used it, I think.  I plan on teaching the signal and then having my students engage in a chatty activity and practice the signal.  If you have other good suggestions on quiet signals please leave a comment I'd love to hear your ideas on this subject.  Make sure you link my blog in your post and write about "quiet signals."