Implement an IR camera

I’m looking for suggestions on how to implement an IR camera. I would like the player to be able to hold up an in-game camera and see on it’s screen what the world looks like in IR. I could have a temperature variable in objects/materials, but I don’t understand how to make the material look different depending on which camera is being used to view it…
Suggestions would be welcome

You need a material with a render target it in, and a camera attached to said in-game camera object that renders into the render target. How you actually process that image to get a ‘temperature’ variable is another question, but I would suggest looking at custom depth.

Do you mean an IR camera or a thermal camera?

IR is simple, thermal is not so simple.

A camera showing heat, im not sure of theecorrect definition. Essentially, coloring the materials based on some property/variable when viewed with one camera, yet looking normal when viewed with another. Since my in-game imager is made up of a camera rendering to a texture, both the real scene and the texture for the thermal view need to be visible in the main camera.
like this (which they call an ir thermal camera)

I know how to do the camera rendering to texture bit, but not the effect itself.

So, any suggestions?