I used to use a whisper phone! DIY Whisper Phones~ Children use these to hear themselves as they quietly read aloud. This post has great directions and with pictures that explain how to make them with inexpensive materials.
Make and put on the door - Teach-A-Roo: Ticket Out the Door! This can be used as an exit ticket. You could put critical thinking or math on the door. This gives the students something to do when waiting at the door.