Intercom Systems Tutorial

While intercoms are an important component of security systems, little fundamental training exists to explain the options and their tradeoffs. In this note, we do so, examining:

• Analog vs IP
• Door vs Wall vs Desktop Stations
• Intercom Servers Scalability and Pricing
• Intercom Server Features
• Advanced Integration Options - video, walkie-talkies, building management and more

Analog or IP?

The dichotomy familiar to video also is prominent in intercom systems. For many years, intercom technology was built on analog transmission, and characterises a significant majority of new systems. However, like video, the advantages of network integration has driven IP development.

In general, analog intercom technologies are less expensive than IP for basic, intercom only systems designed for sixteen or less stations. However, IP systems quickly become more cost-effective for widely distributed heavily integrated larger deployments. The cost advantage of using existing LAN utility becomes a significant source of savings compared to running substantial 'stand alone' cabling for analog systems.

Intercom terminals

Intercom stations are built for use in a variety of situations. While all types accomplish similar basic functions, different designs are optimized to where they are deployed. Below are pictures of the three most common form factors:

Door Stations: Because intercom are often situated at entry locations, door stations are the most common type deployed. Door stations often include a weather-proofed, vandal resistant inclosure that has an amplified speaker. Ambient outside noise often requires the speaker run at higher volumes than more discrete 'wall stations'. Door stations often include additional features like card readers and keypads as well as basic call button features to support integrations with access control or telephone systems. Prices for door stations range between $50 to $850 depending on transmission format, enclosure type, and speaker/microphone/component quality.

Wall Stations: These are the most basic, and often least expensive, type of intercom stations. Wall stations are typically mounted indoors, and they are typically unsealed electronic devices intended to mount in single gang electrical boxes. Plastic face plates cover non-amplified or line powered speakers, and controls are limited to a single 'call button'. These units are installed to facilitate voice communication from one inside area to another. For example, wall stations are commonly employed on the unsecured side of a secured door, and act as a two-way doorbell.

Desktop Stations: These are most commonly deployed as 'master' stations, often provisioned to receive call requests from many end stations. Unlike a door or wall station that has limited call routing, a desktop station is able to receive calls from a large number of stations. In a traditional 'manned operator' role, the human attendant can even redirect or transfer calls from desktop stations. These units are often integrated with phone systems or other surveillance platforms to open doors, trigger video recording, or cue up mobile radio responses.

Specialty Stations: Intercom stations designed for explosion-rated environments, parking lot call boxes, and emergency call units in elevator cars are examples of application specific call boxes. The image below depicts common 'specialty' units:

Intercom server

In addition to intercom terminals, most systems require the addition of a central server. Regardless whether a system is analog or IP, a central head end unit is necessary to administrate voice traffic. Unlike video surveillance, audio is not bandwidth nor processor intensive. As a result, standard server builds can handle hundreds of intercom terminals.

Analog servers resemble traditional PBX Phone system equipment and are typically wall-mounted stand alone devices, while IP servers more typically are found installed in server racks and integrated into common LAN networks.

Server or 'head end' prices range from $500 for small system units (<24 stations) to more than $5000 for large (>550 station) servers. For many systems, pricing is not only a function of system size but also integration features.

Like surveillance cameras, intercom stations are licensed on a 'per device' basis. The total number of terminals determine system cost. In some cases, advanced integrations are individually licensed. For example, if a desktop 'master' station integrates intercom traffic into a phone system, additional server licensing may be required.

Intercom Server Features

The server provides functionality beyond simple call routing. Enterprise-grade intercom systems include the following features:

• One-to-One Communication: the cornerstone operation of intercom systems, where one terminal calls another terminal directly
• One-to-Many Communication: modern systems enable communication from one terminal to several others (zones) simultaneously
• Audio Recording: In some cases, server based recording of audio traffic is important (eg: detention cells, interview rooms)
• Audio Surveillance: Alarm or Alerting on noise (eg: hospital nursery monitoring, parking garages) enhance area surveillance and situational awareness
• Call Mapping: Intercom servers used in large deployments are able to provide visual location of a terminal to facilitate response

Advanced integration

Intercom systems perform an integral part in 'tieing together' a number of different building systems. Some common integrations are:

• Doors and Gates - Intercom terminal relay outputs are commonly used to release door locks or operate gates
• Video Surveillance - pushing intercom buttons can start video recording and record audio in VMS software. (See image below.)
• Walkie-Talkies - especially in environments where manned operator stations are not staffed 24/7, intercom system can be configured into the local mobile radio system for 'roving assistance'
• Building Management - Intercom terminals can be tied into emergency telephone trunks and Public Address systems for the purpose of mass notification
• Phones - integrating intercom systems into capital phone systems allows for 'point-to-multipoint' paging and convenient handling of intercom calls. This feature is common in smaller sites or remote locations, where intercom traffic may need to be routed to an outside system for proper acknowledgement.