On further thought, back in the Bronze Age, ca. 1958 or so, a friend of mine attempted to rig up an IR flash using a kit built electronic flash that was a bit of a monster and the IR filter from some WWII/Korea night vision gear. The filter was about the size of the filters for Kodak bullet style safelights. Even though you couldn't see through it, there was a quite visible deep red glow when the flash fired. It was orders of magnitude less disturbing than an open 120 ws flash, but it wasn't exactly 'stealth." Not sure he ever did anything with it but the experiment itself.

(And I dunno, IR works with the dig!t@l stuff if it's designed for it, or has had the IR cutoff filter removed. But with a 760 nm filter, my EOS40D needed many seconds of exposure in bright daylight to catch anything. I don't follow it closely, but AFAIK, the fundamental sensor elements pick up IR readily, but the package includes filtration to seriously attenuate the IR.)