Solid alkaline sensors containing polypropylene (PP) and four different bromocresol purple-based multilayered hybrid sensitive materials (using silica and polymethacrylic acid [PPMA]) were synthesized. The material was used to sense two alkaline vapors: ammonia and volatile basic nitrogen (VBN) from fish deterioration. The sensor performances were analyzed by color evaluation, the mechanical properties were assessed by tensile tests, and the dispersion of the sensitive materials into the PP matrix was analyzed by X-ray computed microtomography. Three of the four composites exhibited sensitivity toward ammonia vapors, with values of ∆E*_ab > 5; however, the sensitive composites showed lower sensitivity toward VBN, with values of ∆E*_ab < 3.5. The samples showed an elongation at break below 5%, which is characteristic of brittle materials. The X-ray computed microtomography analysis revealed that the PMAA-based hybrid sensor exhibited better dispersion in the PP matrix than the silica-based sensor.