Not exactly tripwires and tin cans – How do intruder alarms work?

Feb 9, 2022 | Commercial Security, Office Security

Not exactly tripwires and tin cans – How do intruder alarms work?

As a kid (I won’t tell you how long ago), I used to set up little intruder alarms by hanging old tins from string. They would make a clattering noise if anyone opened the door and alert me to the presence of an intruder. Of course, you had to be in the room, which meant if anyone triggered the alarm, you could see them and decide if they were friendly. When you think about it, the same system still applies to modern intruder alarms. They are triggered, a decision is made if there is a problem, and a response is made. The difference, of course, is that in the case of a modern alarm, the cans are a series of detectors monitoring movement, shocks and sounds, and you would see the intruder through your mobile at the same time as the emergency response team in central control.

How do intruder alarms work?

The easiest way to look at how an intruder alarm works is to show how it will respond in an incident. So, let’s take a hypothetical intrusion and follow it to see which part of the alarm system will respond and what that means in practical terms.

The primary detection method of an alarm system is to monitor sudden changes in the environment. This could be:

  • Door and window sensors: There will usually be multiple triggers fitted around the door or window, and if pulled away from the sensor, it breaks a circuit and causes the alarm to activate. 
  • If a window is broken to gain entry. While this method may avoid triggering the magnetic sensor, it will not fool the glass break (sometimes called smash) detector. These sense the frequency associated with glass shattering or the vibration from the break to trigger the alarm system.
  • If the intruder avoids those two methods and gains entry from another route, they will likely trip an alarm by triggering the PIR or similar movement sensors. These use infrared or sonic waves to detect heat changes or movement in the room.
  • Trip sensors are placed over key areas such as doorways to internal spaces using lasers or similar technology. These tend to be less common these days.

What happens when an intruder alarm is triggered?

Once triggered, the alarm system will signal a central unit to take appropriate action in response. Sound intruder systems have built-in false alarm identification. For example, they will recognise the difference between a cat running through an area and the more identifiable human-sized intruder. They will also sense natural environmental changes, such as heavy winds, as not an intruder threat, resulting in fewer false alarms. 

Responses to an intruder will usually include:Access Control Monitoring

  • A loud and usually visible alarm will go off. This will act as a deterrent to the intruder and potentially alert passers-by to a potential problem. Often people assume that flashing lights and sirens are to raise awareness; however, the key benefit is that they act as a deterrent by warning the intruder that someone, somewhere, is responding to their crime, making them leave the areas as fast as possible. 
  • An intruder alert will be sent. Your remote security monitoring team will be alerted to the potential problem and investigate the situation. The nominated person(s) for the building will simultaneously be notified to confirm whether this is an accidental trigger or an unknown intruder.
  • CCTV can also be used in conjunction with the alarm to track the intruder’s movements and identify them if possible. The security control centre will access the video stream from the cameras, and the recording will start. With the enhancement of cloud-based monitoring platforms, it is now common for the nominated person to also see the cameras on their phone or tablet to help with the identification process.
  • There may be an automatic lockdown. This will mean internal doors and secure areas will go into a more defensible position, while lifts and access systems may be disabled. If there are people still on the premises, they may be alerted to the presence of an intruder and told to follow their lockdown instructions.
  • The owner or security operatives will decide what to do. Based on the situation, either the police will be called or the intruder turned away. The permitter areas and entrances may, for example, be fitted with a talkback system so they can question the intruder to see if they are lost or a legitimate visitor. 

What happens next will depend on the situation and the level of the threat. 

Do you need an intruder alarm?

Intruder alarms work by doing the very thing the intruder hates. If someone is intent on entering a property illegally, the last thing they need is to be recognised or have people aware of their actions. Alarms attract attention, and the CCTV cameras are there to identify the intruder and locate them for the emergency services. All of this is the exact opposite of what the intruder wants. 

JKE Intruder Alarm Installation ImageSo, do intruder alarm systems work? Yes, they work twice. The best response to crime is not to allow it to happen in the first place. A visible CCTV system and external evidence of an alarm will stop most opportunist crimes and act as a deterrent for the career criminal. Secondly, if there is an intrusion, the system limits the damage done and increases the chances of the intruder being caught on the premises. With 20,000 burglaries in November 2021 alone and most businesses faced with 120 hours of lost labour, and a £2,500 bill per burglary, it is reasonable to say that yes, wherever possible, you need an intruder alarm.

It is also worth remembering that your intruder alarm is only part of your overall protection. They should ideally be integrated with things such as your area protection and surveillance systems, your perimeter security and, of course, your fire alarm systems. At the end of the day, the important thing is not how the intruder system works. It should be designed, zoned, and installed correctly by experienced professionals so that it works for your circumstances.

Looking back at my cans and string antics, maybe I was destined to go into security. If I was, I am glad I did because it is an absolute pleasure to know that we are offering peace of mind by protecting and securing premises of all kinds. 

Call us to discuss your intruder, fire, security, and other needs and let’s chat about how we can help.