Reducing Nuisance Alarms

Even a low rate of alarm can lead to complacency

• By Tom Hofer
• Mar 01, 2022

Critical infrastructure sites need reliable, cost-effective physical security solutions. For these solutions to be a success they must reliably detect and deter would-be intruders, enhance intrusion assessment and response capabilities, secure remote and unmanned sites, and, finally, address one of the most prevalent issues with physical security, reduce nuisance alarms.

Nuisance Alarms Lead to Complacency
Nuisance alarms are alarms that are generated when the site's security system is functioning correctly but is being triggered by non-threat stimuli, which may include wind or other severe weather, nearby human or animal activity, or wind-induced vegetation movement.

For operators, even a relatively low nuisance alarm rate (NAR) can lead to problems such as complacency–ignoring real alarms because it is assumed they are false–and increased costs for ongoing repair and maintenance.
Security Starts at the Perimeter: Fence Sensors and Video Analytics
Adding a perimeter intrusion detection system (PIDS), such as a fence-mounted sensor, augments the effectiveness of an existing fence by providing valuable capabilities to detect and locate attempts to cut, climb or lift the fence.

Connected to the site's alarm systems, PIDS can notify off-site security personnel of the intrusion and engage automated deterrent mechanisms such as the strobing of lights at the fence line, increased illumination of the overall site or using public address systems to provide audible warnings.

Video Analytic Solutions
Intrusion attempts can also be detected via video analytics by using either virtual tripwires defined along the fence or area masks. Entry-level analytics use simple motion detection while more advanced analytics use sophisticated algorithms that detect and classify the presence of people, vehicles, and objects while rejecting environmental changes, including wind-induced movement, shadows and small animals.

• Video analytics offer an exciting new set of capabilities that greatly enhance perimeter security at relatively low cost: Supplement fence sensors by providing additional detection capabilities (especially important for low fences, ornamental fences, and walls).
• Determine the direction of intrusions (ingress or egress).
• Provide covert detection (no visible equipment on fence).
• Detect and track people near both sides of the perimeter fences to provide early warning of potential security events before they can occur. This early warning can be used to direct PTZ cameras, so that high-resolution video can be captured of the intruder at the time the alarm (from the fence sensor) is generated.
• Use anti-loitering analytics to detect persons "camped out" near the perimeter.
• Auto-track intruders with a PTZ camera after an alarm is generated (assists in assessment, response, and evidence collection).

A New Approach to Sensor Fusion: The Best of Both Worlds
Both fence-mounted sensors and video analytics are highly developed and mature technologies, but solutions that can further enhance public safety (and offer the potential to reduce operating and maintenance costs) warrant attention.

The concept of sensor fusion technology is not new. The basic premise of combining multiple sensors together to benefit from their strengths while eliminating their weaknesses has been discussed for many years. Historically, this meant a Boolean logic integration between two systems (typically a fence sensor and people tracking video analytics, or a fence sensor and buried sensor installed in parallel).

This approach certainly can work to reduce nuisance alarms caused by well-defined, predicted events.
A better approach is to introduce intelligence into the sensor fusion system by synthesizing low-level data from the separate systems to generate actionable information. More than a simple Boolean logic integration, true sensor fusion analyzes real-time data alongside historical, locational, environmental, and classification data before generating an alarm.

When signal response data is synthesized between sensors from fence video analytic systems, nuisance alarms generated by wind or debris as well as non-threat human activity are virtually eliminated while maintaining the system’s high probability of detection.

True sensor fusion has the following benefits:

• A lowest possible nuisance alarm rate leads to greater system confidence and better response times.
• Improved probability of detection (Pd), as the individual sensors can use higher sensitivity settings and announce disturbance events faster.
• Simplified integration, as the alarm output arrives from a single source (sensor fusion engine).

While advances in perimeter intrusion detection and video analytic technologies will continue to offer exciting new capabilities, nuisance alarms will unfortunately remain an issue. Sensor fusion offers the means to defeat nuisance alarms while maintaining the highest probability of detection.

To take advantage of sensor fusion, electrical providers will need to work with security vendors that have the in-house capability to intelligently synthesis low-level multi-sensor data in order to generate actionable results. The resulting increase in system confidence enables security operators to focus on what’s important, namely a quick and efficient response to real security threats.

This article originally appeared in the March 2022 issue of Security Today.