The article introduces FOREST, a participatory interface prototype for communicating and negotiating urban heat risk at the scale of the shared courtyard. Instead of treating heat as a one-way disaster message or a purely technical indicator, FOREST translates residents’ images, short texts, sounds, and walking traces into evidence cards that record time windows, location anchors, trigger conditions, and lived consequences. The prototype is framed as a hazard-governance method. It asks how everyday exposure, microclimate difference, and care labor can be made comparable and publicly discussable without scrubbing out uncertainty. What the article adds is a public evidence structure that links heat exposure, vulnerability, and response in a form that can support screening, review, and feedback in community-scale adaptation.