What did the staff at the entrance of Nanyuan Airport put on the bag with a small piece of paper?

Detect explosives. After rubbing the note back and forth on the zipper of the passenger's luggage or the edge of the box several times, the security personnel will take it to the special instrument next to it for testing, so as to know whether there are explosives in the bag. According to reports, this instrument is an explosion-proof detector, which is not only fast, but also sensitive. It can detect and check the explosives or explosive devices in the bag through the traces of explosives. This instrument can detect people carrying explosives or people or objects that have been exposed to explosives.