Harry Bloomfield wrote:
on 03/04/2004, Jet supposed :
4 cameras (initially and expansion room) (prolly b&w again)
good IR night vision and resolution
auto sensing and auto recording
DIY-able )

Just in case you do not already know, IR will need some light to be
able to see. Ordinary lights will work perfectly well, IR lights will
illuminate an area invisibly.

Generally not completely invisibly.
The source is often visible as a crimson glow.
Pity thermal IR cameras are not yet cheap.