I was just messing around with a very small permanent magnet (round) stuck to a piece of metal.
The magnet is round, ~6 mm in diameter. I guess 1 mm thick. (I lack precision tools where I am at the moment) The metal is about 5.5 cm long, 0.5 cm wide and almost exactly half as thick as the magnet.
I detected a bit of a sting from it (don't ask me how), so I went to check it with a voltage meter.
There's a very noticeable jump to ~0.6 V, declining very slowly. After I take the voltage meter off, wait a few seconds, and then re-attach it, it has jumped up to 0.6 V again.
What makes this happen? Am I just very stupid and missing some obvious thing here?
This is my setup (sorry for blurriness, seriously bad lighting):
The "metal strip" is a tool from an old lock-picking set. The black plastic is the handle.
After making these pictures, it's now counting up. Over 0.54 V now. (Update after 3 minutes: It's going down again, no sign of stopping)
(Update) I now notice that when I pour water over the part where the probe, the magnet and the metal strip collide, the voltage climbs up again, and after reaching a peak, slowly starts falling again.
(Update on setup with multimeter) As a user in the answers pointed out, my multimeter setup is incorrect. The plugs are plugged in wrong, causing one of the leads to float. I now plugged them in correctly, and it shows the same, if not higher voltage.