Reference
Glossary of intruder detection terms.
Plain-English definitions of the terms used across commercial intruder detection, monitored CCTV, perimeter security and alarm monitoring.
A
- Alarm receiving centre (ARC)
- A 24/7 monitoring centre where operators receive and respond to alarm and video events from monitored sites. Commercial monitoring is delivered through accredited ARCs (e.g. NSI Gold, SSAIB BS 5979 Cat II in the UK; UL-listed central stations in the US).
- Audio challenge
- A live spoken warning issued by an ARC operator through on-site speakers when a verified intrusion event occurs. A high proportion of intrusions are abandoned at audio challenge.
B
- Beam detection
- Perimeter detection using infrared or microwave beams between transmitter and receiver. Interruption of the beam triggers an event.
- BS 8418
- UK code of practice for detector-activated remotely monitored CCTV systems. Defines the design, install and monitoring framework for verified video response.
C
- CCTV detection
- Camera systems configured to detect activity in real time using analytics (typically AI human/vehicle classification), rather than only recording footage for after-the-event review.
D
- Detection layer
- A discrete detection technology within a defence-in-depth design — e.g. perimeter PIDS, perimeter CCTV, building intruder alarm, internal CCTV. Multiple layers detect threats at different stages.
- Dual-path signalling
- Alarm signalling that uses two independent communication paths (e.g. fibre and cellular) for resilience. Required at higher grading levels.
E
- Edge analytics
- Video analytics that run on the camera itself, rather than on a recorder or in the cloud. Lower latency, lower bandwidth and the dominant modern deployment model.
- Event-driven monitoring
- Monitored CCTV model in which the ARC receives video only when an analytic event occurs, rather than streaming continuously. The commercial default.
F
- False alarm
- An alarm or detection event with no genuine intrusion. False alarm performance materially affects operator confidence, response priority and recurring monitoring cost.
- Fence detection
- Perimeter sensing technology mounted on a fence — typically vibration sensors or fibre-optic cable — that detects climbing, cutting or lifting.
G
- Grade (intruder alarm)
- EN 50131 classification (Grade 1-4) describing an alarm system's resistance to skilled attack. Commercial premises typically specify Grade 2 or 3 based on insurer requirements.
K
- Keyholder response
- Response model in which a named keyholder — staff or a contracted keyholding company — attends site following an alarm event.
L
- Line crossing
- Analytic rule that triggers when a classified object crosses a virtual line in a defined direction. The most common analytic rule on commercial perimeters.
- Loitering detection
- Analytic rule that triggers when a classified object remains within a defined zone for longer than a configured period. Effective against hostile reconnaissance.
M
- Monitored CCTV
- CCTV system whose events are continuously or event-driven received by an ARC, where operators verify, audio-challenge and escalate intrusion events.
- Motion detection
- Legacy CCTV detection method based on pixel change between frames. High false-alarm rate outdoors. Largely superseded by AI classification.
N
- NSI Gold
- UK accreditation scheme (National Security Inspectorate) for security companies and ARCs. Required by many insurers for commercial intruder alarms and monitored CCTV.
P
- Perimeter intrusion detection (PIDS)
- Detection systems deployed at the site boundary to detect attempted breach — including fence sensors, beam, microwave and buried cable.
- PIR (passive infrared)
- Sensor that detects changes in infrared radiation across a defined field of view. The dominant intruder alarm sensor for internal detection.
- Police response (URN)
- In the UK, monitored alarm sites are granted a Unique Reference Number giving access to a defined police response. Repeated false alarms can result in URN withdrawal.
S
- SSAIB
- UK certification body (Security Systems and Alarms Inspection Board) accrediting security installers, monitoring centres and keyholding companies.
T
- Thermal camera
- Camera that images long-wave infrared (heat). Detects human-sized targets at long range in total darkness. Used as the primary detection layer on perimeters.
- Tripwire
- Virtual line in a camera scene that triggers an analytic event when crossed by a classified object. Often configured with a direction.
V
- Verified response
- Response model in which an operator (typically at an ARC) verifies the intrusion event — by video, audio or sequential confirmation — before escalating to police. Attracts higher response priority.
- Video analytics
- Software layer that classifies objects and applies rules within a CCTV scene. Modern analytics use AI for human/vehicle classification, line crossing, loitering and zone intrusion.
- Video verification
- Operator step that follows an analytic event — the operator reviews the triggering clip and live feed to confirm the threat is genuine before escalation.
W
- Wireless alarm
- Intruder alarm in which sensors communicate with the panel by encrypted, supervised radio rather than wired cable. Modern wireless meets the same grading standards as wired.
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