Maybe simple but I haven't any experience of this..
Is it possible to use a common PIR surveillance sensor to detect a warm->cold->warm temperature transition?
I know taht the "normal" use in surveillance is to detect an "hot" body crossing the sensor area.
Instead, I would to detect a cold "object" ( 15-20 C. less than the ambient temperature). 
A possible complication is that the cold "object" isn't a solid but really a localized flux of COLD air that rapidly 
cross the sensor area and that may be very near ( from 5 to 1 feet from the PIR).
A real case: ambient temperature 25-30 C. and a cold air flux of  5-10 C.


thanks,
Marco
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