touch-lamps: how do they work?

[Tulkas]

You know the ones, those lamps that turn on when you touch any of the metal places. How do these things work? I can hold a piece of conductive metal and touch it to the lamp, and it doesnt change. I can hold a wet paper towel and touch it to the lamp, and it changes (I just found this one recently, until then skin was the only thing I had found that worked). Also, my cats paws wont work, but his nose will… Surely they are magic.

[Ponster]

Sorry for the quick & boring answer but I need a shower !

answer

[Tulkas]

(for quick reference) this is the answer from the page given:

Touch-sensitive lamps almost always use a fourth property of the human body – its capacitance. The word “capacitance” has as its root the word “capacity” – capacitance is the capacity an object has to hold electrons. The lamp, when standing by itself on a table, has a certain capacitance. This means that if a circuit tried to charge the lamp with electrons, it would take a certain number to “fill it.” When you touch the lamp, your body adds to its capacity. It takes more electrons to fill you and the lamp, and the circuit detects that difference

That explained, why doesn’t it change if I hold my finger on it while another person touches it? Shouldn’t that change the capacitance in the same way?