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Setting Up Alarm Zones And The Reference Point For A Site-Watch Laser

Setting Up Alarm Zones And The Reference Point For A Site-Watch Laser


Affected Roles:  Owner, Administrator

Related Digital Watchdog VMS Apps:  DW Spectrum

Last Edit:  May 27, 2020



The Site-Watch is a powerful sensor for detecting objects and people with high accuracy over long distances, without the need for additional lights, reflectors, or separate transmitters and receivers used by other systems.

Calculating the distance of any object up to 500 meters (1640 ft.) away at 400 Hz, the sensor minimizes the false alarm rate while increasing the successful detection of objects.  To reach the full potential of the system, it is important to know how to create alarm zones and reference points for its intended purpose.

This article will guide you through an example scenario while describing the ideas of virtual fences, alarm zones, reference points, and network alarms.

Supported/Affected Devices

  • Site-Watch 1640ft (500m) Laser Surveillance Sensor

Case Scenario - Marina

To meet the increased number of boats and engine thefts, a large, private marina requires an alarm system capable of detecting intruding boats.  The Site-Watch is perfect for this application.

Surveillance Planning

The position of the Site-Watch should be carefully planned to ensure good functionality and maximum efficiency of the sensor.

An aerial photo of the marina (Image 2) shows that the area can be secured with two sensors.  Both Site-Watch sensors can be placed on the outer bridge to reduce the risk of trespassing vandals.  The chosen locations make it possible to create separate alarm zones for each part of the marina and to set up reference points.

With separate zones for each part of the marina, the surveillance system can be programmed for different actions, depending on the zone where the detection occurs.  For example, Zone 2 and Zone 3 (Image 2) covers a guest harbor, for which the system can be set to always alert the Harbor Master when boats arrive.  Meanwhile, the other zones are only active during night time.

It is virtually impossible to see intruders in the dark, but knowing the exact zone that an intruder is detected in assists security personnel in locating the area more efficiently.  The system can also choose the best camera angles and automatically point a PTZ camera to the location of the object.

Reference points are used to detect tampering.  For example, if someone tries to realign the system or if the weather conditions are poor.

Alarm Zone Parameters

With the units in place, alarm zones are created in the web interface with four parameters – Zone name, Near distance, Far distance, and Alarm sensitivity.  Up to 20 alarm zones and one reference point can be set for each sensor.

  • Zone Name – the zone name is used to ease administration of the sensors.  With multiple units set over a large area, zone names are a quick way of knowing which sensor and alarm is active.  The zone name has a maximum length of up to 30 characters. Be aware that use of special characters will take up more space.
  • Near Distance – starting distance of the alarm zone, measured in meters.  The Near Distance can be set anywhere in the line of site, between 0 – 500 meters.
  • Far Distance – ending distance of the alarm zone, measured in meters.  The Far Distance can be set anywhere in the line of sight, between 0 – 500 meters, but must be greater than the Near Distance setting.
  • Alarm SensitivityAlarm Sensitivity is adjusted with a slider and can be set between 1 – 5.  The sensitivity values are illustrated with symbols – a boat for the lowest sensitivity (1), a human for medium sensitivity (3), and a motorcycle for the highest sensitivity (5).  It is important to choose alarm sensitivity for the intended use to minimize the false alarm rate.

The alarm sensitivity field also includes a checkbox to control alarm behavior if multiple objects appear in a zone.  This is referred to as Multiple Alarms and is enabled by default.  This setting allows the unit to trigger new alarms when previously existing objects remain in the zone.

  • Object Size – Expected object size in the line of sight is measured in meters.  Some objects might spread the reflections in depth (e.g. masts on a boat).  In those cases, this parameter can be adjusted to classify detected objects as one object.  To keep the false alarm rate as low as possible, this parameter should only be higher than one (1) meter if necessary.
  • Object Variance – the maximum allowed change in distance to detect an object before another alarm can be activated.  Object variance is used to allow new alarms in a zone, even if another alarm is still active.
  • Trailing Window – the Site-Watch will analyze sensor data for 0.01 – 5 seconds.  Depending on object behavior, in terms of speed and size, the trailing window can be adjusted.  The sensor will only set off one alarm during the time period of the trailing window, unless the target variance has been exceeed.

A trailing window of 0.5 – 1 second covers most of the usage, but for detecting small and fast-moving objects (such as motorcycles or objects near to each other) the trailing window can be lowered.  When using a reference point, the trailing window can be set to five (5) seconds, ignoring if an object passes the system and only reacts if the line of sight is disturbed for a longer period of time.

  • Trigger Ratio – the ratio of sensor data in the trailing window that is required to be inside of a zone, or to be outside the reference point.  Trigger ratio sets the sensitivity of the sensor.  The trigger ratio should also be adjusted depending on the object speed and size.

With a trailing window of one (1) second and a trigger ratio of 10%, the object has to be in the line of sight for 0.1 seconds.  However, with a trailing window of 0.1 seconds, the same trigger ratio of 10% would require a line of sight for 0.01 seconds.

Below is a table comparing time in the line of sight for objects passing perpendicular to the sensor.  The parameters must be set to detect objects with less time in the line of sight to ensure detection.

Guide – Creating Zones And Actions

Add Zones and Reference Point

  1. Click on Alarm settings in the top menu.  Zone alarms and Weather filter is displayed.

  1. Click on +Add zone.  The zone setting will display on the right.

  1. Fill in the zone parameters by specifying the Zone name, Near distance, Far distance, and Alarm sensitivity.  Click the Save zone button to apply the settings.

  1. Repeat Steps 1 – 3 for additional zones.  Zones can be edited by clicking on the zone.

  1. Add a Reference Point by clicking +Add reference point.

Set the Distance and Alarm sensitivity, then click the Save button to apply the settings.

  1. Add actions for the zones.

By clicking on the network icon, you can set URL connection alarms.

By clicking on the connector icon, you can set relay actions.

The icon will fill with color while in use.

Connect to URL

Select the VMS (Video Management System) from the dropdown list.  Choose other if your system is not listed. 

Depending on the VMS system, input parameters may appear differently than displayed in this article.

  • Alarm enable – the URL to connect to at the start of an event.  Distance data and uptime can be attached by adding %d for distance and %u for unit uptime (in milliseconds).
  • Alarm disable – the URL will to connect to at the end of an event.

Relay Action

  • Relay time – sets the time the relay is switch on at the time of the event.

  1. Repeat Step 6 for any additional zones and for the Reference Point.
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