There are SWIR, MWIR, and LWIR cameras among IR cameras. SW is just regular camera with the filter removed and they can't see heat. Somewhere between SWIR and MWIR are uncooled IR cameras that use MEMS heat sensor ish arrays built on top of a camera sensor that can actually see heat by differentiating between previous and current frames, with the caveat that they cannot do it indefinitely but must use a mechanical shutter to periodically cool down to operational conditions.

MWIR and LWIR cameras are often cooled and uses more exotic sensing mechanisms, sometimes even vacuum tube based, nowadays usually semiconductor based but not regular CMOS. Some require mechanical shutters obscuring view every other frame(that, I think, is where BHOT/WHOT switch came from; it must be switching whether to show odd or even frames).

You need the MEMS types or better to see heat; they're more often referred to as thermal cameras than IR cameras. They are also unable to see through regular soda-lime glasses, that might pose its own challenge as well.