>[ http://de.wikipedia.org/wiki/Hornwerk_%28Instrument%29 
>[ (my translation):
>[ "In the Middle Ages such instruments were installed in special horn
>[ towers within the fortifications of cities and monasteries.  They
>[ filled a function similar to a siren by, for example, acoustically
>[ signaling to the population the beginning and end of the workday."

The translation Robbie made was fine, but maybe it's good to extend
the information a little bit for better understanding.  The common way
of signaling the population was bells -- in church towers, or on top of
the roof (monasteries, farmhouses, often placed in a small bell tower).

In the Middle Ages there was no need for a signal to mark the beginning
and end of the workday for the population as a whole, but there indeed
were moments that it was necessary to inform the complete population,
especially in times of danger.  Fire was a threat in those times, where
wood as building material was very common, and roofs often were covered
with very inflammable reed.

In cities this alarm signal was often given from towers by wind
instruments, if musicians were at hand and on duty.  Not every town
could or would afford the relatively luxury of city-musicians.

Another example of a signal is the announcement of the closing of the
town gates in the evening.  This is an announcement for the population
and those outside the city who are willing to pass the night inside the
safer city walls.  But it had nothing to do with the end of the working
day -- there was no fixed time for the begin or end of a workday.  If
anything, it was the availability of light, mostly candles and small
oil lamps.

Factories -- or better, shops -- were very small; the owner was one
of the workers and he decided when to start, and when to stop work.
Eventually ruled by guild rules, but not by a "one size fits all"
signal from a tower.

Blacksmiths in cities often were not allowed to start working before
the signal of the end of the nightly watch has sounded.  A blacksmith
can produce quite a lot of noise, and thanks to this rule it was
impossible for him to work during sleeping hours.

At the begin and end of their watch during the night the hornblowers
had to blow their instruments in order to indicate the start and the
end of their watch.  But not of the workday of the citizens.

If "Stadttrompetern" (trumpet- and horn-players in service of the city)
were on duty they also had to blow at fixed moments during the night,
not just indicating the hours, but merely to give an "all clear and
safe" signal.  Those musicians also had to make music in daytime, on
many other occasions, to "illuminate" those moments.

By the way, instruments like the "Salzburg Stier" were not very common.
A lot of towers have been built but very few were meant to be such
"special horn towers", or "horn tower" at all.  If not a part of a
church building, towers primarily were built and used for defence
purposes, and for showing (financial and political) power and importance.
Thanks to the latter the bell tower arose, now seen as the beginning of
mechanical music.

Jan Kijlstra