basic ques 101: do 802.11 cards ping out?

I'm sure this must be answered somewhere or another,
but I looked around and couidn't find it.

Do 802.11 cards in, say, a laptop, transmit
periodic signals when not actively in use
on a wi-fi network?

In other words can such laptops
be detected by someone using (some magic
or another)?

And similarly, when a laptop comes in
range of a network and displays the choices
on its screen, has it already pinged out
various "here I am" responses to those bases
(that is, before you tell it to join up)?

Thanks
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