The intruder alarm – the foundation of the security system

The intruder alarm forms the basis of most security systems, whether in homes, businesses, or other organizations.

Below is a summary of what an intruder alarm consists of and what it can offer the user.

An intruder alarm is a security system designed to detect and alert in the event of unauthorized intrusion into a building or area. By quickly warning of an intrusion attempt, crimes can be prevented and damage minimized. These systems are used in everything from homes and vacation cottages to offices, stores, and high-risk facilities. But how does an intruder alarm work, what types exist, and how do you know what level of protection is needed? This article explains the concepts.

Types of intruder alarms

There are different alarm systems depending on monitoring needs, security levels, and technical conditions. Here are three main types.

Local alarm system

The local alarm is the simplest option. It works independently and activates a sound signal on site—often in the form of a siren—when the alarm is triggered. However, it lacks connection to an alarm center or the internet.

Advantages:

  • Easy installation
  • No ongoing subscription
  • Can deter intruders

Disadvantages:

  • No remote monitoring
  • Less effective for unstaffed premises

Centrally connected alarm system

A centrally connected alarm is linked to an alarm center that monitors the system around the clock. When the alarm is triggered, the event is verified and security guards or police are contacted if needed.

Advantages:

  • Professional monitoring
  • Fast response
  • Suitable for businesses or high-value properties

Disadvantages:

  • Requires subscription
  • More expensive in the long run

Cloud-based alarm system

These modern systems communicate via the internet and are accessed via apps or web services. They provide real-time notifications and can often be integrated with smart home systems.

Advantages:

  • Remote control and notifications
  • Low initial cost
  • Automatic software updates
  • Easy to adapt and expand

Disadvantages:

  • Requires stable internet connection
  • Dependent on third-party services

How an intruder alarm works

An intruder alarm consists of several components working together: control unit, detectors, and often a control panel or app.

The control unit – the brain of the system

It collects signals from detectors, analyzes the data, and determines whether an alarm should be triggered. Functions include:

  • Communication with sensors
  • Event analysis
  • Activation of siren and/or notifications
  • Sending alerts to alarm center or mobile device
  • System monitoring (battery, tampering, errors)
  • Alarm control via panel or app

Detectors – the senses of the system

Detectors respond to motion, sound, vibrations, or other anomalies.

Common types:

  • Motion detectors (PIR) – respond to infrared body heat
  • Magnetic contacts – react when doors/windows are opened
  • Glass break detectors – detect sound or vibration from broken glass
  • Vibration detectors – react to low-intensity attacks like drilling
  • Shock detectors – respond to strong impacts
  • Combination detectors (PIR+MW) – combine technologies for increased reliability

Detection principles

Different sensors use different technical principles:

  • PIR (Passive Infrared) – reacts to temperature changes.
    Advantages: energy-efficient and cost-effective.
    Disadvantages: sensitive to heat sources.
  • MW (Microwave) – emits waves and measures reflections.
    Advantages: can cover larger areas.
    Disadvantages: more expensive, sensitive to interference.
  • Combination Detectors – combine PIR and MW for better accuracy
  • Magnetic Contacts – mechanically simple and very reliable
  • Glass, vibration, and shock detectors – tailored to the threat type and building vulnerabilities

Complementary protection with other sensors

An intruder alarm can often be combined with other types of sensors to provide comprehensive protection:

  • Smoke detectors – alert in case of smoke or rapid temperature rise
  • Gas sensors – warn of dangerous gases such as carbon monoxide
  • Water detectors – detect water leaks, for example in kitchens or laundry rooms
  • Temperature sensors – used in environments with sensitive equipment, e.g., server rooms

What are security grades?

In the European Union, intruder alarm systems are classified and certified according to harmonised standards developed by the European Committee for Standardization (CEN). These standards ensure a consistent level of security and reliability across member states and are particularly important for professional installations and insurance-related applications.

Security grades

Grade 1 – low risk

Suitable for premises with a low risk of intrusion, such as garden sheds or storage rooms.

Requirements:

  • Basic detection (e.g. magnetic contacts, simple motion detectors)
  • Audible-only systems (no remote signalling)
  • Minimal tamper protection

Grade 2 – moderate risk

Suitable for homes and small businesses where there is a moderate risk of theft.

Requirements:

  • Enhanced detectors with some anti-masking features
  • Alarm transmission to a mobile device or monitoring centre
  • Tamper protection and backup power supply

Grade 3 – high risk

Designed for commercial premises with valuable assets (e.g. electronics stores).

Requirements:

  • Advanced detectors, including anti-masking and dual-technology sensors
  • Comprehensive perimeter and internal protection
  • Certified alarm transmission to an Alarm Receiving Centre (ARC)
  • Regular system maintenance and inspection

Grade 4 – very high risk

Intended for high-security environments such as banks, military sites, or data centres.

Requirements:

  • Maximum redundancy and multiple signalling paths
  • Continuous supervision of all components and communication links
  • Real-time monitoring and the highest level of tamper resistance

Product certification – EN 50131-2-x series and beyond

Each component of an intruder alarm system (e.g. detectors, control panels, sirens) is tested and certified according to its respective part of the EN 50131 standard (e.g. EN 50131-2-6 for passive infrared detectors).

Certification is typically performed by accredited third-party laboratories such as VdS (Germany), AFNOR (France), or IMQ (Italy). Certified products receive a mark indicating compliance with the relevant grade and standard.

System design and installation – EN 50132, EN 50136, and national norms

In addition to product certification, the design, installation, and maintenance of systems are also regulated:

  • EN 50132 – CCTV systems in security applications
  • EN 50136 – Alarm transmission systems and protocols
  • National standards may complement EU norms (e.g. PD 6662 in the UK, which adapts EN 50131 for British use)

Installers must adhere to these standards to ensure systems are compliant, insurable, and effective.

Certifying installers and monitoring centres

As with products, installation companies and Alarm Receiving Centres (ARCs) must meet strict requirements. Monitoring centres are often certified under EN 50518, which sets standards for operational, physical, and technical aspects of monitoring services.

Summary: harmonised protection across Europe

Selecting the right alarm system in the EU involves more than just choosing the right hardware – it requires understanding compliance, integration, and the appropriate security grade. The EN 50131 framework provides a consistent approach to aligning security needs across borders, whether for a holiday home or a high-security facility.

By working with certified products and qualified professionals, you ensure that your system is effective, reliable, and compliant with insurance and regulatory requirements throughout the European Union.