Nasturtium seeds are the easiest to see. They're large, about the size of a pea, not in pods, usually in groups of three like a pawn shop symbol. If they're tan and beginning to wrinkle, they'll germinate. I've had success with picking them green and just scattering them where I want them, or letting them dry and then tossing them around.
Impatiens have pods which spring open and shoot the tiny seeds with force. The first time I realized this was when I put my hand into a plant in the summer and thought at first something had stung me, but it was just the pods shooting out the seeds when my hand "set them off". The pods are green, sort of triangular, at the end of the stem, and they explode before they ever turn brown.

Thank you. I'll search again tomorrow in the sunshine

Yep, that's why one common name for Impatiens is "Touch Me Nots." Pods spring open.

Thank you. I found them. Although they were on my neighbors flowers, he wasn't home...he'll never miss them!