I have been asked for something to get attention by those students who cannot raise their hand or cannot raise it high enough for the teacher or E.A. to notice. I recently discovered the Personal Pager from Adaptivation. It has been around for awhile and distributed by Bridges Canada ($170).
This switch-adapted pager has a range of about 23 m (75 feet), is battery-operated (AA batteries), completely wireless and very compact. The button is switch-adapted and the receiver can emit a chime or vibration.
Students in Engineering at the University of New Brunswick are currently developing a personal pager with enhanced features. Their prototype may become an alternative in the future.