What level of security is required?

Different levels of security require different types of equipment. For example, access control used on a meeting room door may not need to provide a high level of security. However, considerably higher security might be needed on the main entrance to a company's premises.

Key pads, or digital entry systems, provide the lowest level of security. They involve individuals keying in a pin code on a door-mounted terminal. Security levels can be increased by giving everyone a different pin code, changing these regularly and placing a limit on the time taken to open the door.

Cards or tokens offer a higher level of security. They can be swiped, held up to or detected by a reader. It is possible to duplicate cards containing a magnetic strip, while other technologies are more secure. The more secure technologies traditionally used have included Weigand, Microcard and Watermark, but proximity cards are now often chosen for new systems.

Biometric systems offer an even higher level of security. These employ an electronic memory to store the unique patterns of the user's fingerprint, hand, retina or iris. The user places their eye, hand or finger on or in front of a sensor which allows entry if the pattern is identical to that stored in the system's memory.

Security levels can be increased by combining two access control methods. Philip Gater, chairman of the British Security Industry Association (BSIA) access control committee and technical director at TDSI comments: "Though pin codes may be a simple technology, when used in association with another technology such as a card, they offer a much higher level of security."

In certain circumstances, where legitimate visitors do not have automatic authorisation, it may be appropriate for an individual to monitor those seeking access and authorise entry, for example in relation to people visiting an office building or maternity ward. Selected entrances are linked to a central control point by a two-way intercom. A video element can be used to combine verbal interrogation with visual recognition.

A variety of factors, other than desirable security levels, also influence system choice. Think about the number of doors and buildings involved, as this will impact on the use of computers and networking.

A limited number of doors could alleviate the need for a personal computer to manage the system. In such cases, the most straightforward solution, would be a stand-alone controller at each door where changes to access clearance can be made as and when required.

However, as Robert Harvey, technical director at PAC International, points out: "If you go from a small system to more doors, it becomes problematic to have to keep going to individual doors to add and delete keys. Things will start to get out of control gradually, and this is the point where a central administration system is needed, whether it be a simple keypad or a personal computer.

"If the system is to operate at a large single site, multiple facilities or across the country, you then have to think about the communications infrastructure. Options include direct connections, radio, local and wide area networks. Often some of these will already be available and the end user will be keen to maximise their investment."