<p>This study reports the development of a dual-system freshness indicator that visually signals raw beef (blade steak) spoilage via color changes as well as a mobile application to detect these changes and, consequently, assess freshness. The indicator comprises an agarose-based sulfur-containing compound-responsive indicator incorporating myoglobin and a polyvinyl alcohol-based pH indicator with alizarin, and its applicability for monitoring beef freshness was evaluated. When the total volatile basic nitrogen values and aerobic plate counts of beef reached their spoilage threshold values, the colors of the sulfur-containing compound-sensitive indicator and pH indicator changed from brown to red and from purple to orange, respectively. The indicator effectively tracked spoilage caused by sulfur generation and pH changes. Furthermore, the mobile application accurately detected the color shifts of the indicator, enabling rapid and straightforward freshness assessment. The indicator and mobile application have potential for application in the market for the indication of beef spoilage.</p>