Security camera through PVS14 https://youtu.be/gEWniEhtE2k
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.
I've converted cameras (DSLRs) to IR, and you use a replacement IR-pass filter. The IR-blocking (default) filter looks like a piece of blue glass. The IR-pass filter looks like a piece of black glass.
NOTE: It's not perfect. The DSLR image processors and calibration systems are calibrated to the IR-blocking filter. Stuff doesn't work the same, once you convert.
Cheap cameras are best, as they don't have too much precalibrated stuff.
I converted a Nikon D70s, and it still works great.
The dim purpleish glow from a remote that is seen through [many] digital cameras would be quite bright if this IR filter weren't in place.
It doesn't have to be that way, but it usually is that way anyway -- as a design intent.
Cameras used for surveillance, meanwhile, often lack these filters. They're designed with more of a focus on getting any kind of image at all, including when working with infrared illuminators in the absence of visible light. Some even have mechanical elements that move filters out of the optical path for night mode.
This differs tremendously in comparison to a camera that is designed to produce very beautiful visible-light photographs.
(This all conspires to mean that IR is kind of a non-starter for this sort of cell phone camera hack.)
Though the bigger issue with my theory is that while most cell phone and webcam devices have IR filters, many surveillance cameras intentionally do not.