Door Intercom Tutorial

Published Feb 29, 2012 05:00 AM
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Door entry systems are an often overlooked subsystem of facility security. Typically, entry systems are installed on doors with little thought of integration to the overall security systems of a facility. However, proper integration can provide gains in security and overall functionality, for little additional cost. In this note, we overview door entry system fundamentals including telephone based, closed and network intercoms plus integrating them to other systems.

Telephone-Connected Intercom

This type of intercom is connected to the facility's phone system, using either analog telephone line or station ports, or VOIP. Users answer intercom calls via their telephone handset. The door may then be released via a dedicated button or via DTMF (touchtone) code. Viking is the best-known manufacturer of doorphones.

The main advantage of answering intercom calls via phone is that no other hardwire is required, simply a free port on the phone system. This also means that multiple parties may answer the call, at no additional cost. Users of proprietary intercom sets must install a substation at each staff area where calls are to be answered, adding cost. The main disadvantage is that if a user is already on the phone, they must put their current call on hold to answer the door. For businesses with heavy call volume, this may be a serious issue.

Vandalproof doorphones can be found online for $200 and under for audio-only versions, or $350-400 with internal camera. Models may be found below these prices, but generally offer little in the way of vandal or weather protection.

Closed Intercom

In a proprietary, or closed, intercom system, the door intercom is matched to one or more inside stations which are dedicated to answering calls. The number of door stations and master stations varies from system to system. Some may only support one-to-one communication, while others support many-to-many configurations. Aiphone is perhaps the best-known manufacturer of this style of doorphone.

The proprietary intercoms dedicated master station is both an advantage and disadvantage. On the positive side, it may be operated more simply, since it is dedicated to the task, and has limited functions. Typically, answer and door release functions are clearly labeled, and easily accessed, so no codes must be remembered, as with telephone-connected systems. However, each master station adds cost to the installation, typically in the amount of a few hundred dollars. If answering duties are handled by a group of people, this may easily add upwards of a thousand dollars to a system.

Simple audio-only intercoms may be found for as little as $100 online, or less. Adding video to the intercom increases price substantially, to around $600 and up. Note that these prices are for 1:1 systems, with a single door station and single master. Additional stations are sold separately.

Network-Based Intercom

A recent development, network-based door intercoms replace, or complement, dedicated master stations with software loaded on staff PCs. Other options convert intercom door stations to connect to encoders, allowing calls to be answered through the VMS system. These options both allow calls to be answered more easily from multiple locations, as any PC with speakers and a microphone may act as a master station. This also eliminates the cost of multiple master stations, essentially providing the advantages of both telephone and closed intercom systems. The Aiphone JKS-IP is an example of a this style of intercom.

Connecting the intercom to the network does come at a price. The JKS-IP, for example, which connects an Aiphone JK master station to the network, sells for over $1,000 online, approximately twice the price of a similar kit without network connectivity. However, with additional master stations in the range of $250-300, not including installation costs, connecting to the network via the JKS-IP is much more attractive if multiple locations need to answer calls.

Video vs. Voice-Only

After deciding on the type of intercom, the second fundamental decision is whether to use a video or voice-only intercom. Generally speaking, door intercoms with cameras built in will provide the best image of a caller, as the camera is closer to the subject, and intended for this purpose. In cases were cameras are already installed watching an entrance, they may be used to view subjects instead, in conjunction with an audio-only intercom. Some closed intercoms allow analog cameras to be fed into the system, displaying these images on the master station in place of a camera located in the door station itself. 

Integrating to Surveillance Systems

In most cases, door entry systems are treated as standalone systems, separate from the surveillance system. Integrating the intercom system to a VMS system is generally simple, however, with two general means:

  • In most cases this is accomplished via an encoder, which accepts an analog video feed from the camera, and a contact closure from the station's call button. The contact closure is used to call up video on live monitors, if desired, to bookmark video for quicker retrieval later, or other functions. 
  • In cases where an IP camera with a reasonable view of the door already exists, such as in a lobby or just outside a door, the call button is tied into the camera, as in the case of the encoder.

Very few door intercom systems are equipped with IP cameras which may be directly integrated to VMS systems. This is beginning to change, with the Mobotix T24 door station and Commend's WS200 series. However, neither of these options are well-integrated to VMS systems, with the video stream only generally supported.

Regardless of which of the above options is used, there are definite benefits to integrating them with a site's surveillance system:

  • Record of visitors: First and foremost, integration provides a record of visitors to a facility. Since internal cameras in door stations are intended to provide the clearest shot possible of the caller, these images should be more than adequate for identifying subjects if need be.
  • Automation: Tying the intercom's call button into the VMS allows for other events to be triggered upon button press. Cameras surrounding a loading dock or gate may be activated and called up on a monitor, or to move a PTZ to a preset position. This allows security staff to verify a caller identifying as UPS is actually in a UPS vehicle, for example, or that they are not accompanied or tailgated by unknown parties.

Typically, cameras on-board door intercoms do not need to be recorded or viewed 24/7. They provide tight views of subjects which may not be useful for general surveillance. For this reason, recording is normally performed on motion only, or on event, tied into the station's call button. 

Integration with Access Control Systems

When installing intercoms on access-controlled doors, best practice is to trigger door release through the access control system. This is accomplished by wiring the intercom's door release relay to an input on the access control system, which in turn fires the relay controlling the door's lock. If the door intercom directly releases the door, it could result in forced door alarms and other errors, as the access control system is unaware the door is being released. This integration also provides a log of when the door was released, which may be useful in investigations.