Product design for an IoT smart monitoring product for short-term rentals, across a mobile app and a web platform: sensor pairing and setup, push and in-app alerts, a live noise trend against the limit, guest messaging, quiet hours, team roles and the first run. This is a self-initiated sample with placeholder data, not client work. 19 screens (12 app, 7 web) go from grayscale wireframes to a clickable prototype to final visual designs on 89 tokens, set in Inter. A sample usability round with 5 placeholder participants and 4 tasks produced 5 findings, each shown before and after. A consistency audit counted from the screens takes terminology mismatches between app and web from 3 to 0. The handoff has tokens as CSS variables and W3C design tokens JSON, 45 component states, redlines, 25 SVG icons, 38 layered SVG frames and 8 questions for the development team.