Wireless systems have many advantages, including unobtrusive installation, high nodal densities, low cost, and potential commercial applications. In this study, we fabricated a radio frequency identification (RFID) based wireless sensor system using carboxyl-functionalized polypyrrole nanoparticles (C-PPyNPs). The wireless sensing system consists of two parts: an RFID reader antenna as a wireless signal reader, and a C-PPyNPs coated ultrahigh-frequency (UHF)-RFID tag as a sensor tag. The C-PPyNPs are synthesized through chemical oxidation co-polymerization and are covalently bound to the tag to form a passive type sensor. This wireless sensor has a very high sensitivity to ammonia at a distance and detects concentrations as low as 0.1 ppm. It also maintains detection performance when deformed by bending and twisting. This sensor can be used for wearable technology for gas detection due to its flexibility.