VS121 sensor supports counting the number of people who crossed a defined virtual line, then upload the count value according to the reporting interval. Before testing, please ensrue your VS121 sensor firmware version is and above.

Recommanded Height

For line crossing feature, the recommended height is more than 3m (the optimum height is 3m) for standing objects.

Illuminance Requirement

We recommend that the illuminance is greater than 50Lux. Besides, when the illuminance is between 20~50Lux, we recommend disabling WDR function; when the illuminance is >50Lux and the scene has a clear contrast between light and dark (such as a corridor), we recommend enabling WDR function.

To know the illuminance of the current scene, you must use an illuminance meter, or you can refer to the following common environmental illuminance values:



Indoors at dusk


cloudy indoor


sunny indoor


Recommanded Installation

  • Make sure the sensor is facing straight down, in line with the ceiling.
  • Make sure there is sufficient white light on site.
  • Avoid getting very strong light, like sunlight. 
  • Make sure there are no moving objects interfering in the counting area. For example, do not install the sensor too close to a door. 
  • Avoid installing the sensor near a mirror or avoid drawing the line to the mirror.


Operation Guide

You can refer to below videos to know how to configure the line crossing feature and how this works.

Line drawing notes:

1) The arrow direction of the detection line depends on your drawing direction.


2) Ensure the detection target can pass through the detection line completely. It’s recommended that draw the detection line perpendicular to the In/Out direction, and make the line on the center of detection area without other objects around. 


3) A redundant identification area needed to be left on both sides of the detection line for the target. This is to ensure that the sensor has stable recognition and tracking of this target before it passes the detection line, which will make the detection and count more accurate.