Soliaree, maybe it's a test of if you are able to set boundaries. Maybe as soon as you ask T to stop using the Dinger with you, he will do it and will be proud you set a boundary. Have you asked him not to use it?

My T sometimes asks me, "what can I do to make it safe for you?" If your T asks that, you could ask him not to use the dinger.

I noticed that Doc John has written an article on the "Ding" situation, and he does not approve:
Ding! Time's Up!

Maybe this would be a good article to print out and take to your T.