The whole area of alarm generation is growing more sophisticated, with faster communication technologies and new products. This is setting a trend for all installers to become more involved with remote signalling techniques. The future of the intruder industry lies with advanced signalling methods and by expanding in this sector we will establish a secure business structure. However, we should not disregard one serious upgrade issue because, as a signalling medium, it still forms the nucleus of the intruder industry – namely the external sounder.
Alongside the increasing use of remote signalling, the range of audible warning devices has also grown to offer a variety of options and high levels of aesthetics, enabling them to be used on any type of property and at the highest specification. So here we look at a few ways of upgrading existing equipment or selling new lines in order to further these business opportunities. The choice may be influenced by cost and personal preference, but from a security perspective we must also consider the likely risk of attack, audible output and the need for either SAB (self-activating bell powered by the control panel battery in an alarm condition) or SCB (powered by the onboard battery) operation.
External sounders will always be subject to attempts to force them from their mountings, to abuse from hammers and blow-torches or to drilling and then muffling by the injection of insulating foam. I can still recall the days when potential intruders deadened electromechanical bells by pouring plaster of paris into bell box housings through the vents, or even through a hole in the top that they’d drilled with a manual drill – that was before cordless ones had arrived. The intruder would return to the site a day or so later when the plaster had set and break in to the property. This progressed to the tactic of ‘stuff and cut’, by which systems were disabled first by injecting insulating foam into the sounder and then by cutting the telephone line. The introduction of louvreless enclosures, foam sensing beams and more secure telephone signalling that detects line disconnection have all helped to get round these problems.
As time went on, stronger housings with rear tampers, more powerful sounders and higher capacity onboard batteries arrived. Then came galvanised metal backplates and inner covers encapsulated within sealed plastic housings to protect against the most adverse weather conditions. Electromechanical bells and mechanical sirens went into decline in the face of opposition from solid state electronic horns, piezoelectric sirens and mylar cones, which formed new-generation bell boxes with integral xenon strobes.
Security installers can generate new business and benefit from demonstrating to existing clients how the ubiquitous external sounder has advanced over the years and the ways in which the intruder system can benefit from using a new-generation product. Most importantly, it illustrates to the casual observer how home security has been upgraded. The client is also assured that a vital part of their system, which is most on display, is brought in line with modern-day practice.
Box that can blend
In so far as BS 4737 is concerned, the sounder must be of two notes of fundamental frequencies that cannot be confused with the emergency services and be enclosed and weatherproof, offering protection as that of 1.2 min steel. It must generate a minimum 70dB(A) mean sound level and 65dB(A) in any one direction at 3m. It must also be self-powered and have an anti-tamper circuit.
The features of external sounders have grown enormously so that today’s range of enclosures can blend with any environment. There is a full range of sounder options, many colour combinations and comfort LEDs. There are metal cover and backplate options, audible setting confirmations and battery monitors to prevent sounder failure. Intelligent sounders have become available and are engineered to communicate via a serial data link with a panel that has upload/download facilities. This enables complete bell box diagnostics without any on-site attendance. It allows sounder and strobe current measuring with unique algorithms of the signalling with battery voltage measurements and local and remote bell tamper deselection.
‘I only want a simple upgrade’
From the options available we can offer the client an innovative product to whatever level they require when selling new systems. But where does this leave the client who is happy with his existing product and only wants the most simple upgrade? One of the main concerns of clients with an intruder alarm has always been related to the certainty of the system to stop its audible output in the event that it false alarms or malfunctions.
The installation of a new-generation sounder with an SAB or SCB cutout ensures that even if a fault occurs in the hold-off supply the external sounder will stop after a pre-programmed time. A problem with older modules is that they can sound for extended periods of time if the hold-off supply is lost, because it is then no longer able to be controlled by the alarm panel bell duration. The solution to this is to change the module to one with an integrated timer or to add a timer circuit as an interface. These are inexpensive options and present standard minimal upgrades. The diagram on page 55 shows conventional SAB and SCB circuits and how they may be supplemented with a timer module. These timers remove the output voltage after a preset period and automatically reset when the input voltage is disconnected, although the strobe can continue to flash until the system is itself reset.
If in doubt, hide it!
Although the bell box itself is an ideal deterrent and an essential component, by the very nature of being overt it lends itself liable to attack. If the property to be protected is vulnerable and there are problems in making the sounder difficult to gain access to, it is wise to add additional sounders with battery support but at hidden points. Prime examples are behind airbricks or fascia boards, on the inside of signs, or below the eaves of roof tiles but within the loft space. Alternatively, it should be supplemented with additional audible devices. These should be covert but supported by standalone SAB/SCB modules. Mains-powered sounders are capable of extremely high-level audible outputs and can be added to a system by a relay link, but the disadvantage is that they do not have battery support in the event of disruption of the supply.
One thing to be appreciated with audible outputs is that sound does not follow a linear scale but it is of a logarithmic manner, so a sound measuring twice the level of another will not seem twice as loud. Sound levels decrease with distance in proportion and a sounder rated at 90dB(A) at 1m is the same in practice as one rated 80dB(A) at 3m. Most sounders are specified at 1m but a siren placed at a general height of 6m actually loses one sixth of its quoted rating at 1m: 16dB(A).
Take note of trees
Therefore, because the minimum sound level at which a sounder is audible above moderate ambient noise is 60dB(A), the placement of it can be so important. This problem is compounded by the normal temperature gradient where air gets cooler with height. This causes the sound to refract up and reduce the range. Audibility will be reduced even more in areas with high dense hedges and trees or if fixed to non-solid surfaces, as the sound will become badly attenuated.
There are few complications with installation. In the field, it is without doubt easily understood and inherently reliable. Indeed, despite new communication signalling, the audible sounder still has a lot to offer, has a healthy future and remains a good avenue for generating business and upgrading. These revisions are all ideal, benefit our industry and are at no great cost to the client. There is a huge selection of styles to suit any application or the most pedantic of customers, and they can satisfy the level of risk of any system designed for local signalling.
Sales possibilities of sounders remain high and can lead to other system expansions, upgrades or integration with other networks.The external box also allows company images and logos to be screen printed in the most prominent of positions and guarantees the best free advertising. Its days are not numbered just yet!
