When a woman is nervous or uncomfortable, her speech often speeds up. She fills silence, jumps between topics, and sounds scattered. That is not necessarily bad, it can even be a sign of nervous attraction. But when a woman speaks to you in a slow, calm, measured tone, she has relaxed into your presence.
For women, safety is not a nice-to-have. It is non-negotiable. If she does not feel safe around you, no amount of charm or good looks will close the gap. But when she does feel safe, her voice gives it away. It slows down. It softens. She does not feel the need to fill every second.
Pay attention to how her tone compares to how she speaks to others around her. If she is noticeably more relaxed with you specifically, that tells you something real.