One of the neat things about working in so many different classrooms obcserving my students is that I get to experience a variety of ways that teachers get their students' attention. Many have little bells, chimes or gongs, others use a rhyme such as "1 2 3, eyes on me" to which the students respond "1 2 eyes on you", while others flash the lights or use a verbal command.
Every so often I come across something quite out of the ordinary such as the teacher at the Olive school in Arlington Heights, who I worked with many years ago, play the scale on a recorder when she wanted her students' attention. The effective part of this strategy was that she didn't resolve the octave scale until all the children were paying attention. This drove the more musical students in the class crazy and so they would make sure that their peers were soon giving the teacher their full attention so she could restore harmony through the resolution of the octave scale of 8 notes.
One of my current cooperating teachers has a wonderful way of getting her third graders' attention. She says "And a hush fell over the crowd" to which all the students reply "Hush". Isn't that neat?