Communication device for Verbal children?

I know it sounds crazy, and parents with minimally, verbal or nonverbal children probably will hate me for it. However, my son has times where he can’t communicate. He’s either too emotionally overwhelmed, or too much sensory overload. He struggles to get our attention appropriately and often hits or yells. He is in speech therapy.

I’m looking for what the best communication device would be for a child that only needs it in certain circumstances. I don’t want to get an iPad because he will use it to play video games during school. I need something that is dedicated solely to communication.

Does anyone have experience they can help me with?