This post reminded me of a time a few years ago (before I started buying all these expensive flashlights) when I was playing around with a dodgy $5 flashlight and a PIR motion detector. I was flashing it directly into the PIR "window" and it didn't detect it (assuming that I didn't move).
A few minutes ago, I tried using my small range of flashlights on an IR sensor (its a USB remote control receiver for my Digital TV card). I'm not sure if it's similar to how a PIR sensor works but its the only IR sensor that I got. Firstly, my SF G2 w/61 shining directly into the sensor didn't make the receiver's LED blink at all... with a deep red/IR filter, same, no IR detected.
However, when I got my Inova X5t, things were completely different. With and without the IR filter, the receiver was able to detect the prescence of IR from the white LEDs. Quite a strong and consistent signal btw...
Conclusion
Whether or not an IR sensor will be able to detect the IR from a flashlight (I'm guessing) would depend on the sensor's wavelength specifications. I'm sure that the SF is emitting massive amounts of IR in the form of heat... but not the right frequency for the IR sensor to detect it.
Jeff