In Hong Kong at the moment, in one of the more budget accomodations in a relatively run down building (New Lucky House) - and the owner just came to my room with an officially dressed person who wanted to test something in my room using a hand held probe.
Yellow, with a mono LCD numerical readout and two sharp prongs, she pressed it to the wall at a number of random locations and to the grout between tiles, and lights flashed green and red and she noted the readings in her book.
What was the purpose of these measurements? Anyone know?