Different categories
We can broadly identify some different applications for personal attack alarms. Firstly there are shops and commercial environments, secondly banks, post offi ces and cash handling applications – and thirdly high risk environments in terms of physical violence, particularly in parts of psychiatric care, social services and in correctional institutions.
Broadly speaking banks and shops primarily invest in personal attack alarms due to the risk of robberies, whilst in hospitals, within social services and in prisons it is a matter of a risk of physical assaults.

Shops
In a shop environment it is rather common to equip staff with portable alarm buttons, often carried on a string around the neck. This part of the alarm market is exposed to heavy competition. The wireless alarm buttons are often a minor part of a larger alarm installation, and the quality varies. Often single shops buy a personal attack alarm. Then it becomes a matter for the shop to organise a connection to a security company or to the police – which means certain obligations.
However it has become increasingly common today for shops to jointly hire one or more security guards. In various kinds of shopping centres this has almost become a standard solution. For the shop this is usually a favourable solution, because it is then possible to send a milder alert for assistance which is only sent locally to the guards at the centre, as a complement to the full personal attack alarm. The threshold for using such an alarm is substantially lower, as such a call is not being connected to the police. In many cases it is enough for a guard to show up at the entrance and mark his presence for things to settle.
The greatest ”window” in terms of risk of robbery in shops is in the morning and in the evening, often in situations with just a few people in the shop. But predominantly larger shops can also see a risk spread over the whole day, and in these cases an alarm function which gives a silent (vibrating) alert to a senior colleague, manager or a work group, is chosen, often complemented with a position indication of the location within the premises of the colleague that has triggered the alarm. A satisfactory position indication can normally be generated by means of small radio beacons, transponders at the door and similar devices, which the alarm transmitter can detect and be updated by.

Banks
The environment in a bank offi ce or in the case of cash in transit situations diff ers signifi cantly from the one in common shops, as the amount of money handled is so much greater. The closest resemblance in shop environments is the protected cash counting rooms which are common in larger stores.
There are special procedures and alarm systems in place when handling cash, where there is a minute control of the cash in transit vendors in terms of time and positions. In addition they usually move between specifi c, secure premises or vehicles where they are enclosed by ”radio bubbles”. There is a lot of secrecy around these special cases, so we leave them aside in this context.
Bank offices have for a long time been equipped with personal attack or PA buttons. The technology has to a great extent been maintained and instead one has reduced the risk of robbery by making the staff alarms portable. Perimeter protection, for example armoured glass between customers and staff , is a classical solution. Today the banks have started to introduce closed cash handling to a great extent, and as a consequence the bank offices have become more open. The tactic is to remove the cash by means of technical solutions – and to a certain extent also delay the action from for example the police. The aim is to avoid a situation where hard pressed robbers remain in the bank, with the increased risk of hostage taking, exchange of fire in dense urban environments and similar situations.
A robber is normally not interested in harming staff, which is why the portable alarm devices are not an essential part of the protection. On the contrary it may expose the staff to greater risk – if a robber knows that there is an alarm triggering device clipped to the belt of the staff.
Going back to cash-in-transit situations, staff often release the containers to a robber, but ensure that the content becomes unusable by means of colour ampoules and also making the content traceable by means of a transmitter.

High risk environments
The environments where advanced, portable staff alarms are mostly in use are work places where staff frequently are exposed to concrete and unpredictable risks of ending up in threatening or violent situations. This is mostly the case in hospitals (particularly in psychiatric care units), social welfare offices, prisons and similar institutions. The conventional hospital alert systems are similar in kind, in spite of the fact that they are used in a slightly different way – to bring attention in case of medical emergencies rather that assault situations.
A personal alarm for high risk environments normally has multiple functions. In addition to manual buttons for assistance and attacks they are, in most cases, equipped with a rip-cord, which triggers if someone tries to remove the transmitter. Often they are also equipped with functions like ”man-down”, which triggers if the carrier and the device are laying on the floor, as well as a movement detector which triggers if no movements are detected within a preset number of seconds.

”The frequency of garage opening devices”
Radio transmission in a wireless personal attack alarm can be designed in many different ways. The most basic systems contain alarm transmitters using any of the frequency bands around 433 or 868 MHz where no licences for the equipment are required.
The frequency band around 433 MHz has been used for alarm transmission for a relatively long time. Unfortunately there are no regulations about how the transmission is to be performed, which has made the radio environment appear to be disorganised. Some people call it the ”Garage opener frequency”, and such a radio environment can of course be questioned if one intends to install attack alarms where demands on operational stability and protection against false alarms are especially high. In places where this kind of alarm system has been installed, false alarms are called ”cake alarms”. Anybody who can’t manage his alarm device properly – and forces his colleagues to come to assistance unnecessarily – will simply have to buy a cake for the coffee the following day.

The standard frequency
In the frequency band of 868 MHz there are established sets of rules and regulations. Around 868 and 869 MHz there are in total three different frequency bands which can be used for alarm transmission, something which has led many manufacturers to adopt and design systems for these frequencies, particularly in the last five years. If one purchases a wireless system working in this frequency band it is essential to carefully check the quality of the radio equipment.

Alternative frequencies
There are also some manufacturers using a substantially lower frequency band. An interesting solution used in several more advanced wireless systems, is to separate alarm transmission and reception. The transmitter could, for example, use a licensed frequency around 169 MHz – which used properly offers a better range than when using higher frequencies. A triggered alarm is then distributed to the other alarm transmitters via a totally different frequency, for example a licensed frequency around 429 MHz, another range specifically devoted to alarm transmission.
This method is generally somewhat more expensive, but on the other hand these frequencies are less crowded as the suppliers need to apply for a licence for the use of these frequencies from the relevant authorities.

IR- and ultrasonic alarm systems
The classic IR- and ultrasonic alarms can in orthodox terms also be included in wireless alarm systems. They offer some advantages: primarily that the alarm devices are relatively cheap to purchase. There are however substantial disadvantages with this kind of system. Firstly there are several frequently occurring noise sources. IR-alarms can for example be affected by bright sunlight. In a similar way, ultrasonic alarm systems can be affected by noise from ventilation systems and other systems of a similar kind.
The most serious problem is however that these kinds of alarm systems are limited to the room where the receiver unit is mounted. In a hospital environment it is thus necessary to install receivers in every area where this type of alarm maybe required.
In many cases there is no need for a completely new cable installation, as the receiver unit can be connected to an existing (cable based) alarm system. Nevertheless the limitations are major. This is the prime reason for many hospitals, at least in sensitive departments like general admission, departments for drug addicts, and psychiatric departments, to buy radio based alarm systems, in spite of the fact that they are more expensive to purchase.

Alarm distribution
Another relevant issue in this context is the alarm distribution. This affects all situations where staff alarms are installed. In case the alarm sounds, flashes or beeps it is essential to quickly establish where the alarm is coming from, and possibly also to identify who is in trouble.
The conventional hospital alarm system can also serve here as an example. When somebody presses the alarm button there is a visual indication by means of a light in the corridor above the door to the room in question. Often, additional indications are also turned on making it possible for staff some distance away to determine the direction to go in, to find the right corridor and the right room.
This becomes of course much easier with portable alarm transmitters with a built in display window, which in the confirmation process displays the room number or zone – and possibly also the identity of the individual raising the alarm. How quickly the distribution of an alarm is transmitted to colleagues is of course a very critical issue. This is a matter of technology, and in this aspect the traditional analogue alarm system is still going strong. When the alarm gets to the central unit or to a sub central within the system it will immediately be transmitted to all receivers in the form of a broadcast message which all alarm transmitters in the vicinity can catch. Ideally not more than a second or two is needed before all affected staff have been made aware of the incident.

Risk of serious problem
Nowadays digital alarm systems are often chosen, and many of them work brilliantly. However in cases where it is necessary to integrate these alarm systems with other functions there is a real risk of running into serious problems. This applies especially when the alarms are to be transmitted via systems for DECT-telephony and when the alarm should be distributed as quickly as possible to many people.
In such situations the alarms are usually distributed as individual calls throughout the system, which can lead to bottlenecks, especially if the system depends on base stations which are mounted inside the premises to act as repeaters for each other.
If an acknowledgement is required from every receiver then the situation could arise where the system continues to transmit to every receiver until the acknowledgement comes and in the meantime blocks further distribution of the alarm to more receivers. This problem has until now not received a lot of attention, but could and can result in unacceptable delays in the distribution of alarm.