Natural polyphenols found in health supplements and drinks have antioxidant and anti-inflammatory properties. In particular, to determine the beneficial qualities of antioxidant drinks and beverages, consumers demand precise quantification of the total amount of polyphenols as on-site detection. Herein, we developed a new concept of portable beads suitable for the field detection available: colorimetric quantification of polyphenols equipped with color converting software applications in a smartphone or tablet PC. The yellowish beads contain ferric ions to react with polyphenol to produce blackish metal-phenolic complexes. It is simple to perform the detection procedure: dipping the beads in the analytical sample and out-taking a photo-converting into RGB color values and quantification of the existed polyphenol. The overall process was completed within 5 min. Compared with the Folin-Ciocalteu assay, which is a representative optical sensor kit for total phenolic content, the bead-based sensor showed a better limit of detection of 0.0415 mM for tannic acid and comparable sensing capability for a polyphenol-containing plant extract and brewed tea. The beads conserved the shape and sensitivity after months of storage or under environmental interference such as a change in the temperature.