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Last edited 12 May 2021
Intruder alarms detect attempted intrusion or unauthorised entry into a building, room, site or secure installation and trigger a response. Well-fitted and maintained intruder alarms can make organisations and individuals less likely to become victims of burglary, vandalism and other forms of attack.
Intruder alarms can be wired or wireless. Generally wireless alarms are easier to install. Installing wired alarms can be disruptive and even domestic installations will generally need to be fitted by a professional.
Bells-only alarms, also known as 'audible alarms' make a loud noise when they are triggered. This is intended to alert nearby people to a potential intruder and to scare off the intruder. Unlike monitored or speech dialler alarms, there is no guarantee that any form of assistance will come, and in urban environments, alarms are often ignored.
A speech dialler or 'text alert' system will call or text nominated phone numbers. Contacted 'keyholders' may then take action, either investigating themselves, or notifying another respondent. They then may be able to remotely access CCTV cameras or microphones within the premises to monitor the situation and determine what sort of response is required.
Alarms may be monitored commercially, sometimes as part of a wider contract for installation and maintenance. The alarm connects to an alarm receiving centre (ARC) when triggered. The receiving centre will generally first ring the building and ask any respondents for their password identification. If this is incorrect or if there is no answer, they may inform the nominated keyholder(s) or respond themselves, or may notify the police.
Because of the number of false alarms, the police will only respond to alarms with a police unique reference number (URN). To be given a URN, alarm systems must be installed, maintained and monitored by a company listed with the National Security Inspectorate (NSI), or Security Systems & Alarms Inspection Board (SSAIB).
The police accept 3 types of new installation:
- Sequential: The first alarm notifies a keyholder. A second, different alarm in a designated period will notify the police.
- Audio: The alarm activates microphones allowing the alarm receiving centre to listen for any criminal activity.
- Visual: The alarm activates CCTV cameras allowing the alarm receiving centre to look for any criminal activity.
The required type of alarm, security grade, type of signalling and response an be determined by undertaking a risk assessment. The risk assessment process should involve consultation with the insurer of the premises. Certain types of cover offered by insurers may be conditional upon the level of protection given by the intruder alarm system. This may for example require remote signalling to an alarm receiving centre, keyholder response, and police response.
- Grade 1: Not adequate for insurance purposes.
- Grade 2X: Suitable for lower-risk homes.
- Grade 2: Higher-risk homes and some lower-risk commercial premises.
- Grade 3: Commercial and high-risk homes.
- Grade 4: High-risk premises.
Ideally there should be at least two keyholders available at all times responsible for responding to alarms, preferably in pairs. They must be highly-trustworthy individuals who should be able to attend within 20 minutes, should be contactable by telephone and have their own transport.
 Related articles on Designing Buildings Wiki
- Access control.
- Carbon monoxide detector.
- Commercial security systems.
- Construction phase plan.
- Entry control.
- Fire and rescue service.
- Fire dampers.
- Fire detection and alarm systems.
- Glass break detector.
- Health and safety.
- Heat alarm.
- Joint fire code.
- Noise nuisance.
- Perimeter security.
- Security and the built environment.
- Smoke detector.
 External references
- Association of Chief Police Officers, Commercially Monitored Remote Signalling Intruder Alarms for Police Response.
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