If you are a light sleeper, and the reindeer make a clatter on the roof or Santa calls out to Rudolf or Donner and Blitzen, then you’ll be all right. When you hear Santa Claus and co, just open the window and look out. But suppose it’s quiet, or you are dozing – you’ll miss the chance to see the magic of Christmas. That’s why you need your very own Santa Claus & Elf Detector.
Now here is a curious thing. A high-sensitivity multimeter, with its leads connected to nothing, set to AC, will in general display a reading, often 100mV or more. Just the probe wires lying around will pick up a signal. And that signal isn’t constant – move a bit closer to the meter to read it and the reading will change, like as not. What is going on here? Quite often, it is the magnetic field around wires carrying current – wires in the wall, wires to lights in the ceiling, wires in transformers will all do it to some extent. This AC magnetic field will induce a small voltage...