You must have a quick, easy, effective way of getting your students' attention. It has to be something that you can use over and over all day long. . . Try out a few different ones, and then choose one that you can stick with. Students can SEE it from anywhere in the room. Students can HEAR it when they are interacting in teams.
Students know how to spread the quiet signal to others.
Room should be quiet within 3 to 5 seconds. If it takes longer, it's not working. Teacher holds up one hand and slowly counts to 3. Students look at teacher, hold up one hand, and put finger to lips to signal others. Room must be quiet by the count of 3.