I am always asking if they heard me and I expect them to respond, if not, I assume they are not listening. If someone keeps going "oh" I wouldn't even guess they are not listening.
When I speak to my husband, I ask him if he heard what I just said when he doesn't say a word and he goes "yeah I heard you."
Also if other people are talking, chances are they not not listening to a word you are saying. Same as if another person is talking to them and chances are they may not be listening to you if you start speaking to them. If you are talking to someone and then another person comes and starts talking to that person and that person starts to talk to them, chances are they are not listening to you.
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Son: Diagnosed w/anxiety and ADHD. Also academic delayed and ASD lv 1.
Daughter: NT, no diagnoses. Possibly OCD. Is very private about herself.