The detection of rosiglitazone (RSG) in food is of great importance since the excessive intake of RSG could cause adverse effects on the human body. Although liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry are the preliminary methods for the detection of hazardous materials in food, they are not suitable for point-of-care or on-site detection. Herein, a time-based readout (TBR) device with an application software (APP) controlled by a smart phone was developed for the sensitive and selective immunoassay of RSG. The homemade TBR device was based on a two-electrode system, where the immune molecule-modified glassy carbon electrode was used as the bioanode, and Prussian blue-modified FTO was used as the cathode. By using Au-modified octahedral Cu2O with high catalytic activity as mimetic peroxidase, an insulating layer was generated on the cathode by catalyzing 4-chloro-1-naphthol (4-CN) into benzo-4-chlorohexadienone (B4Q). The time to reach a fixed potential varied indirectly with the concentrations of RSG and was recognized by the APP, while the electrochromic property on the cathode was also correspondingly changed. Under optimum conditions, both the square root of the time and the chroma value of the electrochromism exhibited linear responses for the detection of RSG ranging from 5 × 10-10 to 5 × 10-7 g/L, while the limits of detection were 8.2 × 10-11 and 1.3 × 10-10 g/L, respectively. With easy operation and portability, this TBR device showed a promising application for point-of-care monitoring of hazardous materials in food or the environment.