Rain bees?
 

Bees behaving badly is s sign of rain
http://www.abc.net.au/news/newsitems...1/s1800208.htm
And apparently bees have been trained to smell out explosives. Then they
roll up their probiscus to let their "handler" know that they have located
the explosive.
Only thing now is to make a video camera to see what the bees are doing and
projecting it on a computer, and possibly make a program to recognise this
behavior, then alert the handler.
You could have bee stations all over the airports etc.