Dial to open

A function available on GSM intercoms, or a GSM relay. When the SIM card number is dialled, a relay will operate, usually to open the door. In some cases the relay will only respond to known 'White list' numbers. 

PoE - power over ethernet

A function of ethernet switches. Devices plugged into a router or switch derive their power from the switch, so a separate power lead is not required. Videx IP panels and monitors accept PoE.


Access controls and intercom panels have one or more output relays to operate a gate or door lock.  A volt free relay means there is complete isolation between the output contacts and the rest of the device. This pretty much ensures universal compatibility. Relay contacts can be described as NO normally open, or NC normally closed. It describes the switch state in the untriggered state. NC contacts are only used for locking magnets or safety circuits.  A relay is a magnetically operated switch. An opto relay is a light operated switch.

PSU (power supply)

Electronic items need a power supply. Audio intercoms and access controls are normally 12V. Video intercoms are often 20V to 24V. True 2 wire systems use a special 35V power supply. Just because the voltage matches, a supply may still not be suitable. There is current to consider, ac or dc or even regulated. Using the wrong supply can damage the equipement to which it is connected.

Analogue or digital

A digital signal has two voltage levels indicating ON or OFF, 1 or 0. Analogue signal voltages vary with the voice or video signal. If a digital signal degrades over a long distance it can be restored. Analogue signals cannot, so are more prone to interference. The 2300 system is completely digital, so can work on only 2 wires.

Video signals

Old analogue video used to travel down special coaxial cable. These systems are still supported, but not for new applications. They were replaced by analogue balanced video, where two wires would send the same video signal, but down normal cable. Digital video has taken over for quality and convenience. Shortly it will all be wireless using wifi.


GPRS, general packet radio service, is protocol for send data across mobile phone networks. While your cell phone is within range of a mast, it is ready to receive data and respond to it. It is the basis for IP intercoms.

GPS is completely different. Global Positioning System invented by the US military to find an electronic device via satelite from anywhere.


Cat5 and Cat6 are ethernet cables with 4 twisted pairs of wires 0.22mm. Not only good quality, but high suitable for high rate digital data, and inexpensive with direct burial versions. Each core is a single strand.

CM2 is a Videx spec' for true 2 wire intercoms.

YY cable is mains rated, multi-strand control cable with several core sizes and numbers of cores.


A locking magnet, or 'maglock', has an armature plate that is magnetically 'locked' to the magnet side. Monitored magnets have an embedded sensor that detects when the magnetic field is completed, that is when the magent is in contact with the armature plate, and the power is applied. The sensor effectively detects that the door is fully locked.


Anti-tamper measures are attributes applied to an access control device on the public side of a security door. It raises an alarm when the device, such as a standalone keypad, is under attack. It is most important where access to the wiring could be made to unlock a door. Raising the alarm could disable the unlock process before illicit entry is affected.

A card reader, or serial keypad sends data to a processor on the secure side of the door. Breaking into the wiring would be of no benefit, so there is no need for anti-tamper measures.


RTE 'request to exit' or PTE 'press to exit' refer to buttons. A door with access control to enter a secure area often has a button on the secure side to get back out.

When a door strike is activated, it usially stays unlocked until the door is returned closed. A locking magnet is silent, and could re-lock as soon as power is restored. Therefore, exit buttons for maglocks frequently have a timer built in (typically 5-10 secs) to allow the door to be pulled.

Form A, B, C

A relay described as having a 'Form A' contact has is normally open (N/O). A 'Form B' contact is normally closed (N/C). Most access control devices are 'Form C' which is N/O and N/C & Com.


A mortice lock or maglock is designed to be flushed into its surround. Most door strikes are mortised into the corner of the door frame.

Shear magnet

An standard locking magnet approaches the armature plate head on.  A shear magnet approaches its armature from the side. Naturally, there needs to be a few millimetres clearance, so the armature is spring loaded. When the power is applied, the armature plate is pulled towards the magnet. The power of a normal magnet is in the magnetic flux, which is compromised by alignment and dirt. Shear magnet strength (when engaged) are the material's shear strength.