This is mend as a handy tool to warn you for possible ESD risks.
Whenever you approach this small circuit with charged objects (like plastic bags) the LED will start lighting up. After a few seconds of inactivity the LED will slowly dim again. If you move antistatic bags in front of it, it will not respond.
The minimalistic design uses only a JFET (transistor), a diode and a LED. It can detect a small charged plastic bag moving at a distance of 50cm. Over 25 of these circuits were build already. The circuit works best with the specified components.
(SMD versions shown here but also through-hole versions could be used)
For normal use a simple detector wire of a few cm is sufficient but you can add aluminium foil to the detector wire (see picture) to increase both the sensitivity and the optical effect.