This is a sort of complicated idea to put down in words, so I'll do the best I can:
When a certain type of element hits the "detector" it sends an electrical current (but only if a battery or other external power source is attached to the detector).  This would be useful for say, smoke detectors.  You put a small sample of SMKE into the detector, so it knows to detect that element later.  The DETC can be used to activate E-walls to release water and put out the fire.  This is only one small thing that could be done with it.