This design-led study explores how circular economy principles can be embedded in research prototyping while comparing environmental sensing methods. A reusable outdoor prototype, deployed in three contexts, combined embedded sensors and API data. Using proxy indicators (energy, material mass, emissions) and end-of-life planning, API sensing indicated a far lower impact, while embedded sensing offered hyper-local data. All prototype components were either reused or repurposed, demonstrating circular prototyping in practice, with findings intended as design-informing rather than definitive.