Thermometers,　one　of　the　most　commonly　used　instruments　at　home,　are　normally　adapted　to　measure　temperature　directly　with　high　accuracy　but　rarely　adopted　to　act　as　readout　in　the　biosensors.　It　is　necessary　to　find　some　ways　to　establish　a　relationship　between　the　concentration　of　the　target　and　the　temperature　change.　In　this　study,　a　common　thermometer　was　used　as　readout　to　develop　a　convenient　immunosensor.　The　designed　immunosensor　comprises　three　components,　including　target　recognition　area,　water　flow　system,　and　exothermic　reaction　bottle.　The　capture　antibody　for　the　target　[carcinoembryonic　antigen　(CEA)　was　selected　as　a　model　target]　was　preloaded　on　the　bottom　of　the　recognition　area.　In　the　presence　of　CEA,　a　sandwich-type　structure　was　formed　between　the　capture　antibody,　CEA,　and　biotinylated　detection　antibody.　Then,　the　streptavidin-functionalized　platinum　nanoparticles　were　labeled　on　the　detection　antibody　due　to　biotin-avidin　interaction.　The　captured　platinum　nanoparticles　can　effectively　catalyze　the　decomposition　of　H2O2　into　O-2.　The　continuous　production　of　gas　resulted　in　pressure　increment　inside　the　reaction　bottle　and　further　pushed　the　water　flow　into　the　exothermic　reaction　bottle.　Finally,　the　water　reacted　with　calcium　oxide　to　generate　a　large　amount　of　heat　in　the　exothermic　reaction　bottle;　thereby　the　temperature　inside　the　bottle　was　enhanced　and　recorded　by　a　common　thermometer　easily.　The　temperature　enhancement　has　a　linear　relationship　with　the　CEA　concentration　in　the　range　of　7.81-500　pg/mL　with　a　detection　limit　of　0.6　pg/mL.　Furthermore,　by　taking　advantage　of　simplicity,　compatibility,　stability,　and　high　sensitivity,　our　temperature-based　immunoassay　has　been　applied　to　detect　CEA　in　human　serum　samples　with　satisfactory　results.