How do your alarms communicate?
There are many ways that a signal from a fire or burglar alarm can reach the receiver; from POTS (the telephone line that you talk on every day) to sophisticated radio transmitters that seem to have been designed for the CIA to cellular service. Whatever method your security system is using, the important function is to get the correct data from the device (motion detector, heat detector, door contact, etc.) to the base station where dispatching occurs.
The oldest method is the regular telephone wire. In the older systems, each account leased a copper wire connecting them to alarm company central station via the local telephone company switching station. Developed in the 1870’s to measure changes in current at a box in a store or home, it is still used by many private customers. One problem is that the communication flow depends on a solid connection between the two points – if a wire is cut on a pole, the earliest systems show an alarm. Over the past few years, telephone companies have begun to phase out this type of service, since maintenance costs are high and switching equipment is dated.
The answer is derived channel monitoring – where the phone company provides a special device at the switching station and another at the alarm company. The digital signals are then monitored by the phone company for quality control – so line faults can be reported and alarms transmitted more securely. Please note this system is an option: not available in all areas of the country.
A third source may use a cell-phone similar to what you probably carry with you today. It was marketed in the 1980’s and allows the alarm user to transmit data on the same system that local cellular phone companies provide. There is a charge, of course, as you are paying for the phone number and usage. A typical system has an alarm control interface, a cell phone mounted in a cabinet with back-up power, and an outside antenna if needed. This device allows for alarms to be transmitted even if local phone service is down, providing that it can “hand-shake” with a cellular tower site. Upgrades are ongoing, such as the same technology that allows you to operate your laptop computer in the car. (Telemetry)
Another plan of action is radio, again this is a newer technology developed in the past twenty years. The simplest type simply substitutes a two-way radio (such as your officers use in the field) to transmit alarm information from one building to another instead of a phone line. This requires a dedicated radio channel as well as line-of-sight reception. A better solution is becoming part of a commercial network, where tower sites and equipment are maintained by a private company and channels are shared based on repeating the messages from office building roofs, water towers, mountaintops and other elevated locations.
Hardwired alarm panels are less expensive than wireless panels, but they are harder to install. Keep this in mind when working on budgeting for alarm systems. An average alarm installation with a hard-wired system takes about 12-16 hours. A typical wireless installation will take less than 4 hours.
Another consideration is that some types of construction lend themselves well to a hardwired installation, and others will require the use of wireless.
Even if you select a wireless alarm panel, some jurisdictions still require that the device back-ups are hardwired. These typically include the power transformer, the electrical ground wire, the telephone connections and any keypads/arming stations and audible alarms.
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The main difference between a hardwired and a wireless alarm panel is how each one communicates with the protection devices connected to the system. A hardwired panel will require a wire to each “zone” or device on the system, while a wireless system utilizes a radio frequency to communicate with the “zones” or devices that are connected to it.
While a normal electrical circuit is a Parallel Circuit, a typical hard wired alarm circuit is a 2-wire normally closed loop with end of line supervision commonly referred to as a Series Circuit.
A Series Circuit allows electrical current to flow from the alarm panel, down one wire through the alarm initiating device and back to the alarm panel. When the current is interrupted, the panel will register a fault on the circuit/zone. End of Line (EOL) resistors are added to the circuit so that the alarm panel can supervise the condition of the zone for ground faults, electrical shorts and open or cut wires.
Multiple normally closed devices can be connected to a single zone by connecting the devices in series, with the EOL resistors installed on the last device in line. This way, the entire circuit is completely supervised from the panel to the last device in line.
When wireless alarm systems first appeared on the market, they were not the most reliable systems around. Most of them utilized non-supervised wireless transmitters to communicate to each of the field devices. A non-supervised wireless alarm transmitter would only send a signal “one way” to the alarm panel receiver when it was activated.
For example, when a door or window was opened, the transmitter would send a wireless signal. The alarm panel would receive the signal and activate the appropriate zone. The transmitter would not send a signal when the door or window was closed, so the receiver/zone had to reset itself after a few seconds. With a non-supervised wireless system, you could actually arm the system with a door or window wide open without even knowing it.
Most new alarm systems utilize a redundant bi-directional fully supervised wireless connection for two way communication between the transmitters and the alarm panel receiver. With fully supervised wireless, the alarm panel can tell you the real time status of a door or window. If a door is open, it will keep the zone faulted until the door is closed.
Most of the early wireless systems were very limited in their addressing schemes. They utilized dip switches with binary addressing (explained later) to differentiate between points on the system.
This was O.K. if your wireless system was installed and commissioned correctly, but what happened when a neighboring location installed the same type of system? If the neighbors motion detector was addressed the same as your dock door, your alarm would go off every time they moved around inside their building. As you can imagine, this could cause some major problems that were very difficult to troubleshoot.
Modern wireless systems utilize serial numbers, binary house codes, or other proprietary technology to assure that only transmitters enrolled into your panel will be received by your alarm system. If you do your research and purchase a good reliable supervised alarm system, you should never need to worry about your neighbor’s wireless transmitter setting off your alarm system.
Another problem with the older non-supervised systems is that you did not know when the batteries in the transmitters are low or need to be replaced. The only way to verify that they were working is to periodically test them.
Because, even the most sophisticated wireless alarm panels are useless if the transmitter batteries are dead, therefore supervised wireless panels are programmed to check in with each of the remote transmitters at least once every 24 hours. If your transmitter has a low battery, the keypad/arming station will immediately inform you of the trouble condition.
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With any wireless security system you should always test the performance of your system regularly. The range of any wireless product can be affected by the environment and the structure in which it is installed. Additionally, the range can be adversely affected by environmental conditions, interference form electrical devices or even the orientation of the transmitter in relation to the receiver.
So who is the winner of this argument? Well, according to Underwriters Laboratory (U.L.), the most secure and reliable installation methods utilize hardwired installations with End of Line (EOL) 1 or 2-resistor supervision. In fact, U.L. approved installation standards for federal government and other high security installations require all zones of protection to be hardwired with complete 2-resistor line supervision.
Not to say that wireless systems are an inferior product. In fact the fully supervised systems offer excellent protection that is perfectly suitable for 90% of residential installations.
If you are considering a wireless alarm system, be warned, there are still systems being sold and installed today that are non-supervised, so make sure that any system you are considering offers complete wireless supervision.
If you opt for a hard-wired alarm system, make absolutely sure that the system is installed with the supervisory resistors at the end of the line. To make installation faster and simpler, some installers will place the resistors in the alarm panel rather than at the end of the line.
While this method provides supervision of the zone for ground faults, it does not provide protection for a direct short or worse yet, someone splicing into the wire and shorting them together which will essentially close the loop so the panel will not see the zone open or close.
Whatever method that your security department chooses to move the alarm information from the point of occurrence to the receiving station, make sure that you can provide interference-free data and your staff is able to interpret and dispatch the information. As technology grows into the twenty-first century, new ideas about alarm transmission will be unveiled and older technology will be challenged by parts shortage, lack of technical support, or noise on the line. This article does not offer any specific vendor names or ultimate solutions – but I hope that you will examine your burglar and fire alarm system with an eye toward data transmission.