ADVANCED COMMUNICATION IN TODAY’S WIRELESS ALARM SYSTEMS

Wireless alarm systems are quick to install. However, the quality of the different systems varies – and so does the requirements depending on application. Modern wireless alarm systems work for example with regular data communication.
We start with the background to this technology and an overview of the areas where these systems are used today.

The use of wireless alarm systems and detectors has become increasingly common in recent years. The first more widespread use of this wireless technology emerged as early as around 1990. In The United States these kinds of systems spread quickly, for protection of building sites, as an example. It took until the end of the century until installations started to take off in parts of Europe. What happened was that several large security companies, like Securitas started to sell wireless alarm system for private homes. Today we can see the results of this. Sales of home alarms to private individuals comprise almost entirely of wireless systems.

Focus on revenues from services
Wireless alarm systems for the domestic market are very easy to install. A control panel is connected to a telephone line or a GSM phone and a few wireless detectors are placed in optional places throughout the home. The customer can in most cases install the system on his own, although there is some risk of detectors being positioned wrongly.
From a business point of view this is no major concern for the security company. What’s important is not the installation itself of the alarm system but to tie the customer to the guarding or monitoring services – which are renewed year on year. Technical installations are getting more and more marginal from a revenue point of view and this trend has been enforced by the introduction of wireless alarm systems. The business concept is similar to the situation where mobile phone operators offer a free phone when signing up for a subscription.

Hybrid systems are gaining momentum
It is however not only in the consumer market that wireless alarm systems can be found. Also in commercial installations it is increasingly common to find wireless technology. In fact there are three or four common types of applications.
Often so called hybrid systems (mixed technology systems) are installed. This is the fastest growing segment in the commercial market. In this case a conventional fixed alarm installation is complemented by wireless technology. One can for example use wireless detectors when an existing alarm system requires some minor additions, or when there is a need for movable detectors.
One example is when detectors are needed in locations where it is difficult to install cable. It can also be a matter of concern for historic buildings or premises where cabling is not permitted. So far there are few installations in commercial premises entirely based on wireless technology. Mixed technologies on the other hand are quite common. In addition to burglar alarm detectors, there are also some manufacturers of fire alarms offering wireless technology.

Temporary installations
Alarm systems for construction sites and assault alarms are other segments of the market where wireless technology has made inroads – and for good reason.
Workplace alarm systems are used in terms of systems installed on machinery, on construction sites and in similar applications. Wireless technology is often the given choice in these situations. It could be a matter of a couple of sheds used for a few months on one site and then moved on to the next site, forest machinery at a lumber site where wireless detectors are connected to alarm transmission via GSM or radio link – or operator alarms used as a personal emergency stop and protection for people working in proximity to hazardous machinery.

Assault alarms
The latter application above is of course closely related to assault alarms, an application where wireless systems today are generally accepted. The conventional alarm buttons under the table are still in use in many places, but when staff in high risk environments need to move around, the trade unions usually demand portable assault alarms. We will return to this issue more in detail in a coming article.

Wireless technology controversial
Many alarm installers have had serious doubts about wireless alarm systems. Most installers have extensive experience in running cable for wired systems, but little knowledge in how radio based systems work and how to design such systems. This is why there has been a marked threshold for the technology. Some installers have resisted the wireless systems entirely, whilst others have accepted them and started to sell wireless systems as a complement.

Watch out for the rubbish!
Like with all new technical devices the quality of the equipment and detectors has varied quite a lot. Due to limited technical experience some installers have chosen to import cheap systems directly on their own, predominantly from China and South East Asia. This has resulted in the market being flooded with different wireless brands where the radio technology under the surface has varied quite a lot in quality. It is thus important to watch out. A wireless detector which is too noise sensitive can soon turn out to be a real bad deal, if it generates false alarms and eventually needs to be replaced.

The first generation
How does it work? After the introduction the development has passed several stages. The first generation alarm systems were designed around very simple, analogue radio systems where signals were sent in plain text between a transmitter and a receiver. The communication was thus not encrypted and worked according to a principle some people used to call “Shout-and-spray”. In other words there was no feed back between receiver and transmitter. It was not possible to send any acknowledgements over the radio link – and it was not possible to supervise the link and to verify that the detector really worked. In some cases the unit was designed to send an alarm indication several times in close succession in order to guarantee that the message got through.
Of course over time people noticed that this was not a good solution. It was not possible to detect any defects in the installation, temporary noise could easily disarm the system – and the lack of a proper tamper protection was of course ominous.

The second generation
This all lead to the development of a second generation of systems where a clock was added to the receiver or transmitter and made the detectors (transmitters) send short test pulses at regular intervals. By programming the system to expect these test pulses at pre-set intervals, for example once per day or once per half hour, a simple error and sabotage protection was introduced, which created an alarm if the test pulse failed to come. But the signals were still sent in plain text, alternatively in the form of a simple current crypto.

The third generation
In order to overcome these shortcomings some manufacturers started to develop a third generation of wireless alarm systems. These were introduced to the market at the turn of the century. Now the step was suddenly taken from passive reception to full-fledged data communication. The transmitter as well as the receiver were built as radio modems, with the possibility to send and receive data. This opened the possibility to send alarm acknowledgements over the link, perform advanced function tests and even to upgrade firmware of particularly advanced alarm detectors directly over the link.
Instead of having to rely on regular test signals the alarm link is open both ways in these systems. When an alarm is transmitted it will be repeated until the controller responds with an acknowledgement. The technology offers in addition the possibility to fairly easily encrypt the link.
The biggest disadvantage with the third generation wireless alarm systems is possibly the price. It is approximately three times as expensive to base an installation on the third generation system with radio modems compared to the first generation’s simple transmitter and passive reception.

USA and Europe dominates
Many wireless alarm systems being sold today originate from manufacturers in Asia, where widespread manufacturing of basic systems with passive receivers takes place. The development of alarm systems based on radio modems takes place primarily in the US and in Europe.

Digital technology more secure
The communication in a typical wireless alarm system takes place over special alarm frequencies. Normally these require no licence, and are shared with any other systems in the neighbourhood. When the wireless alarms were introduced most of the systems used the frequency band around 433 MHz, but in later years a new band has been introduced around the frequency of 868 MHz.
On the one hand the reach is better in a system working at 433 MHz, but it requires a longer antenna and the transmitter requires more energy. For that reason most manufacturers of today have switched frequency and build their transmitters for the frequency band of 868MHz. As wireless alarms get increasingly popular this radio frequency band is getting crowded.

”The attack time”
In this context it is important to note that it is better to buy an alarm system which doesn’t require the radio link for longer than necessary. Some people talk about the so called “attack time” which means how fast the alarm communication over the radio link is. With long attack time the risk increases for radio noise or competition from other systems nearby. It is also important to buy a system working with digital communication over the alarm link. In the past it happened quite frequently that analogue signals created positive interference, thus adding the signal strength of each together, which in unfortunate circumstances meant that the alarm receiver activated and indicated a false alarm. With the demand for a digital bit stream in order to activate an alarm this problem is avoided.

Extended range
with repeaters
Another phenomenon which begins to show up nowadays is the possibility to connect wireless units in a chain and make them work as repeaters to each other. In doing so one can overcome previous range limitations. Depending on design one can say that the alarm link typically can manage a point-to-point connection of maximum 500 meters.
When connecting the units in a chain one gets closer to the kind of data communication which exists in the data networks of companies. Here all traffic gets an address and a fixed (static) routing table is established which is distributed to the units of the net. The table tells the radio units how to handle an incoming alarm signal – depending on the receiver address.
A system of this kind can for example be used for installations in large department stores, shopping centres, public transport and similar applications.