Sean Breheny wrote:

> In fact, the voltages involved in these little shocks gotten by
> touching a door knob can easily be in the megavolts, or so I have
> read.

  Kilovolts, actually.  These sparks are three or four millimetres long.
Played with the Ultor connector from a B/W TV?  Half to an inch; ten to
twenty kilovolts.  Not recommended with colour TVs.  A "mini" Van der
Graaf generator about ten inches; 150 to 200kV.  Megavolts (mains line
testing stations including really BIG Van der Graaf generators) and you
are looking at six foot bolts.

  Very approximate, depends on humidity and contact shape.  Points
produce such a "spray" of discharge that they won't allow a high voltage
to be accumulated at all.  And Van der Graaf generators are now obsolete
in favour of Cockroft-Walton ("ladder") multipliers using comparatively
cheap semiconductor High Voltage rectifiers.

  An ionisation source forms a sort of "very sharp" discharge point.  I
hadn't considered this before.  My experience of cheap smoke detectors
is that they are rubbish, a couple I bought and stored for a year
insisted on beeping intermittently even though I could not fault the
batteries and even put in new ones.  Others lasted a few years then
karked.  Is this other people's experience too?  I'm not impressed, but
now I have some ideas on what to do with the old ones!

  Cheers,
        Paul B.