Intercom systems

An intercom is personal telecommunications device which facilitates the exchange of messages between two or more locations where standard vocal communication would be difficult or impossible due to distance or obstructions. Basic intercom systems have been in existence since about a decade into the twentieth century if you only consider designs reliant on that rather handy invention of Alexander Bell’s; the telephone.
Even earlier technologies, similar in concept if not execution to the modern intercom, were fairly widespread. They were particularly prevalent in large businesses, military installations and vessels, as well as stately homes and palaces where they were frequently used to convey instructions to out-of-earshot workers, soldiers and servants respectively. I am of course referring not to strange contrivances of rope and bells, or smoke signals even, but to “speaking tubes.” These were little more than lengths of hollow metal piping which had the handy property of conducting sound for great distances; think of the water or heating pipes in an old apartment building which transmit every unwanted sound.
Even such instruments as the telegraph and the familiar children’s toy consisting of two cans or cups connected by a length of string can be said to have more in common with the modern intercom than the telephone in that they form a closed rather than open system of communication. Of course, such crude methods have nothing on modern intercom systems, which took another leap forward in terms of sophistication with the advent of the new wireless intercoms. Present-day intercom systems are as varied in their forms as their uses. Uncomplicated two-way devices are employed for such functions as access control for the gates and doors of homes, shops and businesses. Once a visitor has announced his or her presence over the intercom the occupant of the premises decides whether to let them in or not. More advanced systems will feature video in addition to audio capabilities, allowing even easier and more accurate identification of visitors on the part of the occupant. Conceivably, even further layers of reporting can be incorporated into intercom systems such as, for example, metal detectors and chemical sensors in areas where the need for high security is great.
Voice-activated intercoms or Audio Intercom units are another tremendously useful refinement on standard intercom systems. They have are used to great effect to monitor babies and others requiring attention, who are for some reason unable to operate regular intercom buttons, such as the ill or infirm. Intercoms are of course not limited to two-way communication either.

There is no theoretical limit to the number of individuals who can be connected via an intercom and little practical limit to the number on a centrally-controlled wireless system. Such multiple-point systems are used to great effect in places where announcements and communication are requires, such as schools, supermarkets, hospitals, factories and airports. Not only can one person use such an intercom system to simultaneously communicate to all present, those who have access to the system can use it to keep in contact with one another.