I need a bracelet or pendant to buzz someone in another part of house. Any suggestions?

Yep we use a doorbell (portable)

We use a doorbell. It's plugged in upstairs and mom keeps the button in her pocket. I can get to her in 7 seconds flat. :)

Is Dad mobile? If he is normally in a chair or bed, then a stationery noisemaker like a bell or jingle bells or a bicycle horn, etc. that he could pick up as needed should work. If he is mobile, carrying those things around probably wouldn't work.

Something portable that wouldn't make noise or be terribly inconvenient for Dad is a coach's whistle. I used one of those while I was recuperating from surgery -- worked slick! Is your father able to blow hard enough for that?

My husband was mobile throughout his dementia journey, and he wore a life alert wrist band. Once he needed help and couldn't make himself heard. He pressed the button. I got a phone call asking me if he was OK. Oh goodness ... I didn't know, I'd go see. I could help him with what he needed and told the monitoring company that. Kind of a round-about way to get my attention, but it worked!

How about either an old fashioned bell that he can clang, OR a bunch of large jingle bells that he can pick up and shake if needed? I think either of these sounds would be distinctive enough to be heard throughout the house without scaring anyone.