>>> 2021-03-06 the fire telegraph (PDF)
I have previously mentioned that, to my knowledge, perhaps the earliest widely used urban-scale digital telecommunications system was the fire telegraph. I'd like to expand a bit on the fire telegraph specifically and urban telegraph networks in general.
Electrical telegraphy as a communication technology was largely developed in the early 19th century and by the late 19th century reached a state that would be fairly familiar to us today---morse code sent over long-distance lines to pass messages between cities. Most people think only of this case (e.g. the service offered by Western Union) when considering telegraphy, but other more specialized systems were in widespread (in fact over the earlier time period much more common) use than the Morse system.
Railroads were early adopters of Morse telegraphy, but largely adopted it as an enhancement to an already widespread system in which a signalman could press a switch which caused a bell to ring in another signal tower elsewhere on the line. Different cadences of bell ringing were used to express different messages, and like Morse the system was surprisingly expressive. I believe this system still sees limited use in certain places in the UK.
All of this preface is to say that "telegraphy" refers to a wide array of different technologies that share little in common besides the use of electricity over wires to convey a message. Moreover, while we usually associated telegraphy with manual operation (e.g. an experienced operator on each end of the line) , various early semi-automated systems did exist, often based on pulse-coding---essentially similar to the railroad's bell ringing.
The fire telegraph falls into this latter, more exotic category: a semi-automated telegraph system using pulse-coded numeric signaling.
The fire telegraph emerged in the mid-19th century as an extension of existing telegraph developments, and although he was not the original inventor, the concept is inextricably tied to John Gamewell and the Gamewell Company. The technology was slow to take off, but by the turn of the 20th century Gamewell fire telegraph systems had become common in urban areas across the US, and on a more limited basis overseas.
Imagine that you are in the position of a fire chef in an urban area at the turn of the 20th century. Fires in urban areas can develop and spread quickly, making early detection critical to limiting damage. But, there is nothing resembling modern telecommunications, even on a smaller urban scale. There are a variety of schemes that can be (and were) used to detect fires quickly, ranging from fire wardens stationed at street corners to run notes to the fire station to, whimsically, an urban fire tower (often just the top floor of a tall building) from which fire spotters watch for smoke. I once read a newspaper clipping about such a facility in Boston where one of the observers quipped about keeping a timetable of factory hours so that they could judge if a new plume of smoke was just a stationary engine being started for the workday.
Obviously these schemes were generally some combination of labor-intensive and slow. The Gamewell Company offered a compelling alternative.
A small box referred to as a "fire call box," and delightfully made of cast iron styled with a building-esque peaked roof, would be installed throughout an urban area, typically at a street corner every two or three blocks. Inside of the box would be a metal lever called the "hook." When a passersby or building occupant discovers a fire, they simply run to the nearest call box and pull the hook. Practically instantly, a steampunk-esque glass-cased device in the nearest fire station would ring a bell and tap out a pattern of dots on a strip of paper, which the experienced fire fighter can immediately interpret as an identification code for the box from which a fire has just been reported---usually checked against a large map posted on the wall for this purpose.
The technical design of the Gamewell system is fairly simple. Much like a rotary telephone, the "hook" releases spring when pulled which retracts at a governed speed. As it retracts it spins a rotor, which holds a set of pins. Each pin runs by a switch, which momentarily breaks the continuous circuit connecting a neighborhood worth of fire call boxes. Each break in the circuit causes a connected telegraph to mark a dot on a piece of paper (by punch or spark). The spacing of the pins forms a simple code: fire box 1 2 3 would have one pin, a gap, two pins, a gap, and three pins. Someone reading the tape just adds up the groups of dots to determine the box number.
In fact, what I described is a rather simple setup. Various large-city departments set up much more complex systems in which a given box would signal not only the local station but also a central dispatch station, which had the ability to forward the call to other stations as well. Various coding schemes could be used by dispatch in addition to the boxes, allowing dispatch to, for example, indicate the type of severity of the call to a station. This leads to the term "four alarm fire," being, traditionally, a fire signaled by dispatch using four pulses or rings---indicating a particularly severe situation.
As you can imagine, these fire boxes were vulnerable to false alarms. Various methods have been used to address this issue, most commonly just trying to fine anyone who falsely activates a fire call box, but some systems used fire call boxes which required a simple key to activate. The keys were usually distributed to trustworthy persons throughout the area, not just firefighters and police officers but also traffic wardens, business clerks, street cleaners, and in general anyone who hung around the protected area and was deemed unlikely to cause nuisance alarms.
Gamewell systems were "municipal-scale" in that they spanned a city or downtown section of one, using dedicated wiring running along utility poles. Such specialized urban infrastructure was not particularly unusual in the early 20th century. The Gamewell concept was extended (by the Gamewell company itself among others) to burglar alarms as well, and the first remotely monitored burglar alarms used a very similar pulse-coded scheme to report via dedicated wires to a central alarm station.
This came logically from the central reporting of fire alarms, which was also implemented in Gamewell systems as building fire alarm systems became more common. In this case, there was essentially just a fire call box mounted in or on a building that was equipped with a solenoid instead of a hook. When the building fire alarm sounded, the solenoid would release the spring to report the fire to the fire department. This system was in use even in areas with no conventional fire call box system (e.g. street corner boxes).
Locally, Albuquerque had such a system, although I do not believe it ever included streetside call boxes. Various buildings downtown have traditional Gamewell cast-iron fire call boxes mounted next to the fire alarm annunciator, apparently to relay fire alarms to the fire department. Interestingly, one of these buildings is Main Library, which opened in 1975, meaning that the downtown Gamewell relay system must have been in operation fairly late. In fact, newspaper references suggest that the system was being installed or expanded in 1964.
If you would like to check my work, Main Library is a great example as, for whatever reason, the legacy fire alarm annunciator and Gamewell box are located outdoors at the rear entrance.
Another urban-scale system similar in nature to Gamewell telegraphs is the police call system. Police call systems were introduced in some cities to allow police officers easy communications with the station before two-way radios became practical. Somewhat well-known due to "Doctor Who," these were basically streetside telephones that were locked with a key carried by police officers. Some, but not all, systems featured a light (typically blue) attached to the phone which substituted for a ringer. In theory, the station could call a police phone near an officer on the beat and they would notice the flashing blue light and walk over to pick up the phone. Similar systems were (and likely still are in places) used by railroads to reach wayside crews by calling a flashing-light-equipped phone in a nearby relay hut (these often had air horns that they sounded as well) .
Although Doctor Who's unconventional spaceship took the form of a phone booth, most police telephones in the US were manufactured by Gamewell and used small cast-iron boxes nearly identical to fire call boxes, except painted blue and fitted with a swinging front door that revealed a phone handset. Because the two systems were so similar it is not unusual to see "conjoined" Gamewell boxes that are red on one side and blue on the other, containing both a fire call box and a police phone.
These Gamewell systems have an important legacy today. First, a small number of cities, San Francisco and Boston that I know of, still have maintained fire telegraph systems. The San Francisco system is regarded as still at least somewhat useful as it is occasionally used to report emergencies during disasters which made the telephone system unreliable (famously during the Loma Prieta earthquake when a number of fires were reported via a system that still improbably worked in most areas). Nonetheless, it will presumably become more and more difficult to justify the cost of maintaining these legacy systems over time.
On a larger scale, the legacy of Gamewell fire boxes has had a significant lasting impact on the organization of fire departments. In the era of fire call boxes, fire stations would often have a set of pre-prepared response plans filed by the numbers of call boxes. So, when a call came in from a given fire box, the station would immediately know which resources they out to send (depending on, for example, the types of buildings near the call box). This "box" system is still in use today by many departments as a shorthand for fire dispatch. A dispatcher will simply radio "box alarm 1234," and various fire units will know by reference to a chart whether or not that box number requires them, and if so, where they should go.
I would love to provide a list of other municipal telegraph operations but I am not aware of many outside of fire dispatch and burglar alarms, although I'm sure they must have existed in certain cases. Earlier coordinated streetlight systems sometimes made use of a pulse-coded scheme similar in nature to these telegraphs but without humans at either end, based on the principal of a notched wheel in one traffic light control box advancing a notched wheel (or camshaft) in another. In fact, for much of its late life Gamewell was a subsidiary of Bliss Manufacturing, parent company also of Eagle Signal, an important manufacturer of traffic signals in the mid-century.
Today, the functionality of reporting fire alarms to a central monitoring station has mostly moved over to telephone or IP. While the protocols used are somewhat proprietary, they generally need to meet requirements established by UL or FM, which must in turn meet standards established by NFPA. The simplest systems consist of an outbound telephone call to a monitoring center which, when answered, sends DTMF digits giving ID numbers for the alarm, zone, and event. More recent systems typically send the same information over TCP, and are more flexible in terms of failover and detailed event reporting. Less commonly, but especially on university and corporate campuses, dedicated or semi-dedicated fiber optics may be used to interlink fire alarms. UL and FM standards for these systems can be remarkably specific and eccentric, something I plan to write about in the future (along with the general world of in-building burglar and fire alarm systems, which have a long history full of ingenious solutions).
There is no real modern equivalent of streetside fire call boxes, which have been largely obsoleted by cellular phones. University and corporate campuses do often install emergency phone systems which serve a somewhat similar purpose but are more oriented towards deterrence of violent crime than prompt detection of fires. Colloquially known as "blue light phones" (which is to some extent a genericized trademark but also plainly descriptive), these range from conventional analog telephones configured in "hotline" mode (e.g. to automatically dial when removed from hook) to purpose-built call boxes with a large red button and an analog, digital, or VoIP phone implementation. Some of these systems are very sophisticated but most, unfortunately, are not.
 There can be a somewhat blurry line here between telegraphy and the teletype, as teletype is a natural evolution on telegraphy which then naturally lead to automated message processing (e.g. AUTODIN). It's not always clear what is a "teletype" vs what is a "telegraph," although anything employing bitwise digital signaling is more likely to be considered a teletype.
 In a marginally related anecdote, I had occasion to spend some time at a bomb range that, due to mountainous terrain, found their two-way radios unreliable. The solution: a great number of strategically placed telephones in weatherproof enclosures, sometimes just on a post on the side of a dusty gravel road. These are doubly advantageous as explosion-tight phones can be obtained for installation in facilities like chemical plants where two-way radios would not be allowed. If I had my way, we would all just have phones everywhere.