An intercom is a closed-circuit voice communication system. Intercoms are commonly used in singular buildings or small collections of buildings and allow for communication across physical spaces.
Intercoms are self-contained and therefore operate free of the public phone system. Intercoms are generally permanent fixtures in the space that they connect to another via communication and utilize hardware such as walkie talkies, telephones, public access loudspeaker systems, and wall mounted speaker and phone systems. Some but not all intercom systems are also attached to security systems, allowing for access control functions within the intercom itself.
The master or base station of an intercom system is an intercom base which has the capability to make announcements to the entire system and also has the capability to connect with any system within the intercom system. So, although a business owner may wire certain intercoms to connect with only certain others, the business owner him or herself may connect with any and all intercoms within the system.
A sub-station intercom system is a system that is capable of connecting to the main base station (ie the business owner or boss) but is not capable of connecting with any other intercom stations within the system at large. This may be used by, for example, a head of security whom only deals with the business owner directly.
A door station intercom system is a system that is situated at the door of an office or home that is capable of making contact only with the main or base station. The door station may not intercom individual intercoms within a building; it only communicates with one base station). This is commonly used in security systems as a means of controlling access to a space.
A wall mount intercom system is affixed to the wall and generally features either a push-and-talk functioning microphone or a hand held phone set.
A belt pack is a portable closed-circuit intercom system. It may also be referred to as a “headset” and involves an intercom station worn on the belt with an earpiece worn by the individual. Belt pack intercoms are commonly used in stage productions or other situations in which individuals who are on the move need closed circuit communications across space.
A handset is a portable intercom that does not have a headset mechanism attached to it. Instead it functions like a portable telephone or a walkie-talkie.
Many modern office telephone systems offer an intercom function, which allows for a closed-circuit intercom messaging system across desks. In many such devices, the ring that signals an incoming intercom correspondence is different than that which indicates an incoming call from an outside source. The intercom system on a telephone does not utilize the outside phone system.
Many intercom systems are hardwired into a building or set of buildings. However, for installations where hardwiring is not possible or desirable, wireless intercom systems do exists. It should be noted that in the case of wireless intercom systems, there is a risk of interference from other systems.