I'm looking for possible options for a very specific temperature-based sensor, which could be used not just for movement detection (like PIR) but also to detect an object of a specific temperature which would be located within a limited space.
First thing that comes to my mind is the passive infrared sensor, which is (as far as I know) capable of detecting only rash changes in temperature. This would work for me only partially since it is desired for this object to be detected even when not moving around (stationary position).
Otherwise, this object's temperature could be deviating +/- 0.5°C with nominal temperature of around 38.5°C. And the range of described sensor would need to be around 10 meters (much less isn't usable and much more could detect other unwanted objects. Sensor would be exposed to outside ambient temperatures in a mild-range temperature environment, which seems plausible to assume that it wouldn't be disturbed by outside temperature most of the time. The object's surrounding temperatures would be at maximum few degrees lower than the object's nominal temperature.
Its hard to say whether such sensor exists due to so many specifics involved. Or maybe a less sophisticated sensor could be used in combination with complex detection algorithm. Image recognition with machine learning and/or artificial intelligence included would be a little bit too complex for this application.
Best I can think of, that would be relatively simple to implement, would be a PIR-like sensor that would respond only to a specific range of temperatures. However, a condition of detecting an object in its stationary position wouldn't be meet. I'm not sure if something like this exists.