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Introduction to Security Intercom Stations



Security intercom systems are used to provide voice communications between two or more locations for security purposes. Security intercom systems are frequently used between a locked building entrance door and a constantly attended location in the building, such as a manned security control room. In this application, the security intercom system gives visitors a means to contact someone in the building when they arrive at the entrance door. Other common locations where security intercom systems are used in commercial buildings includes loading dock doors and at vehicle gates that provide entrance to the property. In residential applications, security intercom systems are commonly used between the main entrance door and a location within the interior of the home.


Simple Intercom System with One Sub-Station


A simple intercom system consists of one "Master Station" and one "Sub-Station". The Master Station is typically located at the point inside the building where communications is to be received. The Sub-Station is typically located at the point where the communication is to be originated. For example, in an office building, it may be desirable to keep the front entrance door locked, and to provide a security intercom system to allow communications between the outside of the entrance door and the receptionist's desk in the lobby. In this situation, the intercom Master Station would be installed at the receptionist's desk, and the Sub-Station would be installed on the wall outside of the entrance door.


The Master Station provides control of the intercom system and typically includes a station selector switch, talk button, speaker, amplifier and volume control. The Sub-Station typically includes just a speaker and call button. When the visitor arrives, he or she presses the call button on the Sub-Station. This causes the Master Station to ring. To accept the call, the receptionist presses the station selector switch. When this button is pressed, the receptionist can instanlly to listen to sounds at the Sub-Station. To talk to the visitor, the receptionist presses the talk button. When finished speaking, the receptionist releases the talk button to listen to the reply from the visitor. This goes back and forth for as long as the conversation continues, with the receptionist pressing the talk button when she wishes to speak, and releasing the talk button when she wishes to listen. At the conclusion of the conversation, the receptionist presses the station selector switch again to terminate the connection.


Simple Intercom System with Multiple Sub-Stations


In many facilities, there may be a need to communicate with more than location. For example, in the office building described above, there may be a need for the receptionist to communicate with the employee entrance door and the loading dock door in addition to the front entrance door. To meet this need, Master Stations are available that can accommodate multiple Sub-Stations. Models that have a capacity of three, five, or ten Sub-Stations are common.


Master Stations that work with multiple Sub-Stations have a station selector switch for each station. Above each switch is an indicator light as well as a label that identifies the Sub-Station ("Front Door", "Back Door", etc.) When a visitor presses the call button on a Sub-Station, it causes the Master Station to ring, and for the indicator light above the appropriate station selector switch to illuminate. The receptionist can then press the station selector switch for the station that is calling and begin the conversation using the talk button as described above.


Simple Intercom System with Multiple Master Stations

Sometimes, there is a need to receive intercom calls at more than one location in a building. For example, you may wish for the receptionist to receive calls during normal business hours, but after-hours, you may wish for calls to be received at the security control room. To meet this need, it is possible to provide multiple Master Stations, each capable of communicating with one or more Sub-Stations. Communications between each of the Master Stations can also occur if this is needed (for example, receptionist could use intercom to talk with security control room and vice versa).


In most cases, the system is designed so that calls from Sub-Stations are received at all Master Stations. The first Master Station that answers the call handles it and all other Master Stations ignore it. Typically, when one Master Station is in use, other Master Stations cannot be used. The system provides a "busy" indicator light at each Master Station to indicate when the system is in use by others.


Simplex or Duplex Communications


The simple intercom system described above uses what is known as "simplex" communications. "Simplex" communications means that communications can occur in only one direction at a time. In the examples above, the receptionist uses the talk button on the master station to control the flow of communications. The receptionist can either talk or listen, but not do both at the same time.


More sophisticated intercom systems are available that use what is known as "duplex" communications. "Duplex" communications means that communications can occur in both directions at the same time. When using an intercom system that has duplex communications, there is no need for a talk button; once a connection is established between a Master Station and a Sub-Station, a two-way conversation can occur without either party having to operate any type of control. This is a much more natural way to communicate and avoids the gaps in a conversation that can occur when the talk button is pressed too soon or too late.


As a general rule, most simple, inexpensive intercom systems use simplex communications, while more expensive intercom systems use duplex communications.


Handset or Hands-Free Intercoms


Intercom stations are typically available in two versions, a "handset" version, and a "hands-free" version.


Handset intercom stations use a corded handset similar to that found on a telephone. The advantage of handset intercom stations is that they work well in noisy environments and that they provide some degree of privacy. The disadvantage of corded intercom stations is that they are less convenient to use and that they are more prone to vandalism and routine wear and tear.


Hands-free intercom stations use a speaker/microphone that is built into the unit. Hand-free intercom stations are more convenient use and less prone to damage, but sometimes can be difficult to use in noisy environments. Hands-free intercoms stations also offer little privacy.


Some intercom stations come with a handset but are also capable of being used hands-free. These stations have a speaker/microphone in addition to a handset and usually work as a hands-free unit unless the handset is picked up.


Wired or Wireless Intercoms


Most intercom systems have traditionally been the "wired" type that require low-voltage wiring be installed between each of the Master Stations and Sub-Stations. On larger or more complicated systems, this wiring can become quite extensive and may be costly to install. However, once installed, wired intercom systems tend to be very reliable and require very little maintenance. Because of this, wired intercom systems have long been the preferred choice of most commercial and industrial users.


Intercom systems are also available that allow "wireless" communications between Master Stations and Sub-Stations. These systems typically use radio signals to provide the communications path between stations and don't require any type of wiring. The advantage of these systems is that they are quick and convenient to install. The disadvantage of these systems is that they don't work well in all settings, and may not work at all in buildings that contain large quantities of concrete and steel or when there are long distances between the stations. Most wireless intercom systems also lack the features needed for the larger commercial user and are considered to be less reliable over time than a wired system. Because of this, wireless intercom systems are usually best suited for use in private homes and at smaller commercial businesses.


IP Network Connected Intercoms


A recent development in intercom systems is IP network connected intercom stations. These stations are capable of being connected directly to an organization's existing data network. This usually means that the intercom station can be plugged into a nearby network outlet or unused port on a nearby network switch. This can greatly reduce the costs of installing wiring and offers great flexibility in the way that intercom systems can be installed and modified. IP connected intercom stations are well-suited for use in large campus environments, particularly when the campus includes buildings that are off-site.


Door Release Buttons


When an intercom system is used to communicate with a door, it is often desirable to have the ability to remotely unlock that door. For example, if an intercom system is used between a receptionist's desk and a locked entrance door, it is common to provide the ability to remotely unlock the door for authorized visitors. Many simple intercom systems incorporate a door release button into the intercom Master Station specifically for this purpose. This button is wired to electrified locking hardware (such as an electric strike) on the door, and when the button is pressed, the door unlocks.


When multiple doors and multiple Sub-Stations are used, remotely unlocking doors becomes a little trickier. Some Master Stations can use accessory relays that allow the door release button to work in unison with the station selector switch. This allows the door release button to release the door that the station is currently in communication with.


Video Intercom Systems


Intercom systems are available that incorporate video surveillance features. Video intercom Sub-Stations are similar to regular Sub-Stations except that they also include a small built-in video camera that provides a direct view of the person operating the station. Most cameras offer a fixed viewing angle; some cameras can be moved up and down and right and left by the person receiving the call. Video intercom Master Stations are similar to regular Master Stations except that they also contain a small video monitor. This monitor is used to view the image produced by the camera in the video intercom Sub-Station.


The advantage of video intercom systems is that they allow the person receiving a call to verify the identity of the person calling. This can be particularly useful in door control applications where it is desirable to confirm which person is at the door before pressing the door release button.


While most video intercom systems provide a good view of a person standing directly in front of the intercom Sub-Station, they generally don't provide a wide-angle view of the overall doorway itself. In addition, cameras in video intercom systems tend to be only of moderate quality and generally not suitable for use with video recording systems. For these reasons, most organizations who are serious about security don't consider the cameras built into video intercom systems to be a substitute for regular surveillance cameras and generally install both at entrance doors.


Exchange Intercom Systems

It is possible to mix and match simple intercom Master Stations and Sub-Stations to create a relative large system. However, when a facility becomes very large and has  many Sub-Stations and Master Stations, the system can become complex and unwieldy. This can occur in campus settings where there are many buildings and many doors.


To meet the needs of larger systems, "exchange" intercom systems were developed. These systems get their name because a central controller, called an "exchange", is used to manage intercom system traffic. Rather than being connected directly together, Master Stations and Sub-Stations are connected to the exchange. Most exchanges allow the use of both wired intercom stations and IP network connected stations. When a call is placed, it first goes to the exchange, where it is them routed to the appropriate station.


Master Stations used with exchange intercom systems often are microprocessor based and operate using a menu driven system. This also a powerful set of features to be packed into a relatively compact station. The benefits of using an exchange intercom system are many and include:


  • Can be expanded to a practically unlimited number of intercom stations

  • Can carry out multiple conversations between stations at the same time.

  • Can route calls to specific stations based on time of day.

  • Can forward calls if station is busy or if call goes unanswered.

  • Can operate auxiliary relays to unlock doors, turn on lights, etc.

  • Can use plain text to identify stations within operating menus.

  • Can interface with telephone and two-way radio systems.

  • Can interface with security management systems.

  • Have ability to be programmed and controlled using a computer.


As might be expected, exchange intercom systems are considerably more expensive than simple intercom systems and are most cost effective when used at larger facilities. The cost of an exchange intercom system cannot generally be justified at a smaller facility.


"Exchange-Less" Intercom Systems


A new breed of system, called an "exchange-less" intercom system has recently been introduced. These systems use IP connected stations that have built-in processors and memory that allow them to provide many of the features and benefits of a exchange system, without requiring the use of an exchange itself. These systems can offer the smaller user a very capable system at a fraction of the cost of an exchange system. While still more expensive today than simple intercom systems, we see exchange-less IP network connected systems as the wave of the future.


Using Security Intercom Systems to Enhance Your Security Program


In addition to being used for basic communications purposes, security intercom systems can be used to enhance your facility's overall security program. Security intercom systems can be particularly powerful when integrated with other systems such as security management systems and video surveillance systems.


For example, with a fully integrated system, when a "door-forced-open" or "door propped" alarm occurs at at access controlled door, the Sub-Station at that door can automatically  be connected to an intercom Master Station at the security control room. In addition, the camera at that door can automatically be displayed on a video monitor. This allows the security officer to both listen to and see what is going on at the door and possibly give a verbal warning to those who may be violating a security procedure ("Hey, you, please don't prop the door open...").


Security intercom systems, when combined with appropriate signage, can also be used for customer service functions such as providing directions to visitors, allowing employees to request a security escort to their cars, and notifying security of safety violations.



If you have questions regarding security intercom systems, or need help in designing a security intercom system for your facility, please contact us.


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