The RKI FP-31 is a compact, sample-draw formaldehyde monitor built for fast, on-site indoor air quality testing. Using a photoelectric colorimetric method with disposable detector tablets, it reads formaldehyde concentration over a 15-minute (0–1.0 ppm) or 30-minute (0–0.4 ppm) averaging period with no warm-up delay before sampling.

Because its optical measurement isn't thrown off by common cross-interferents like toluene, benzene, carbon monoxide, carbon dioxide, ammonia, or acetone, the FP-31 holds up well in real-world indoor environments where multiple emission sources are present. A built-in sample-draw pump feeds air across the detector tablet automatically, and the digital display stores up to 99 readings with self-diagnostics for the light source, pump, and battery.