Lysosomal　pH　is　important　for　regulating　various　physiological　processes,　and　slight　fluctuations　in　lysosomal　pH　can　induce　many　adverse　effects　on　cellular　status,　such　as　inflammation,　aging,　and　tumours.　Heat　stroke　is　one　of　the　most　serious　causes　of　morbidity　and　mortality.　However,　the　relationship　between　heat　shock　and　lysosomal　pH　values　is　still　poorly　understood.　Herein,　we　introduced　a　colorimetric　and　turn-on　fluorescent　probe　in　the　red　to　NIR　range　for　monitoring　lysosomal　pH　values.　The　probe　can　selectively　accumulate　in　lysosomes　with　a　high　Pearson＇s　coefficient　(0.95),　and　the　suitable　pKa　value　(6.73　±　0.07)　enables　the　probe　to　visualize　changes　in　lysosomal　pH　values　during　the　stimulation　by　chloroquine　and　heat　stroke,　respectively.　©　2025　The　Royal　Society　of　Chemistry.