Despite the
wide range of variations, there is a
method in the madness.
Most countries started to implement their
telephone infrastructure in
the early years of the
20th century, at which time
DTMF tone-dialling
was unthought-of. All telephones worked on the
pulse system, whereby
dialling a number would
make and break a circuit to cause a series of
electrical pulses to travel down the
wire.
When the emergency number systems were first thought up, there were two
main criteria:
(a) The number(s) had to be easy to memorise, and
(b) They should be easy to dial in the dark or when surrounded by smoke
or whatever.
Working on this principle, the first suggestion was "111" -- about as
memorable as anything else could be, and easy to dial even if you couldn't
see what you were doing, as "1" (on an old-fashioned rotary dial phone)
is just one finger hole away from the zero which was always at the
bottom of the dial. Zero itself could not be used as it was used to get
through to the operator at the local telephone exchange switchboard
(this was long before direct trunk dialling came along).
However it was found that the wind blowing through telephone cable
suspended from poles out in the street could sometimes cause a fake
pulse to travel down the wire; it didn't take long before they realised
that having the weather call the police or fire brigade was probably not
a good thing. Another number had to be chosen: in the US they simply
substituted the first "1" with "9" -- 911 -- in the UK they replaced all
the "1"s with "9"s -- 999 -- and in other countries other similar ideas
were used. The Americans apparently investigated the British 999 idea but
rejected it as on a pulse-dialled phone, a "9" takes nine times as long to
go through as a "1" does. 911 was chosen as the fastest, easily memorable
number which didn't cause a host of fake calls.
Many thanks to my grandma who spent all her working life as a
telephone operator and filled my head with all this trivia.