Close Contact Detection for G7

Updated December 15, 2020


Due to the rise of COVID-19, companies are enforcing social distancing rules in the workplace, requiring that workers stay approximately 2 meters (6ft) apart at all times. Blackline Safety offers close contact reports that gather data from G7 devices and the Blackline Connect mobile app in order to map out interactions that have occurred in the workplace.

These reports are incredibly useful for monitoring trends, aiding in investigations and addressing incidents after they happened, but it is equally important to remind device users of the social distancing requirement in the moment a violation may be occurring. With G7’s new close contact detection feature, workers will be warned when they are in close proximity to other devices so that they can take proper safety precautions.

This feature will be made available with G7 firmware version 3.445, planned to be released the week of December 14, 2020.


Bluetooth is a wireless technology standard used for exchanging data between fixed and mobile devices over short distances using short-wavelength radio waves. Blackline’s G7 personal safety devices can transmit and receive Bluetooth signals. These signals can be used between G7 devices to transmit proximity information in real time, without the need for GPS or cloud-hosted computation. A G7 device can be aware of other G7 devices nearby and approximate relative distance based on Bluetooth signal strength.

How it works

When two G7 devices are in close proximity (approximately 2m or 6ft), the lights will flash and the device will vibrate. There will not be an audible alarm so that the user will not be distracted from their work. The LCD screen will also display a “close contact detected” message. The lights and vibrations will continue for 10 seconds to remind the device users that they should be following social distancing protocols and stay further apart. After 10 seconds, the device will go back to normal, and the notification will not persist.


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If a different device user joins others in close contact, all of the devices will get another warning message for the new device that has appeared. Again, all of the devices in close contact will flash and vibrate for 10 seconds while showing the “close contact detected” message on the screen, and then stop.


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If the devices are separated from each other more than 2 meters apart for a consistent 30 seconds, and then brought within 2 meters of each other, the same warning will occur again.


Technical details


Warning buffer time

There will be about a 5-10 second buffer before this warning occurs. Bluetooth scans 1s out of every 5s, so the time of the buffer period is dependent on when the device enters the “close proximity radius”. This buffer period ensures that the devices will not get excessive amounts of warnings simply by passing by each other.


Warning message priority

This warning is considered low priority compared to other events on the device. The warning will not be shown during — and will be overridden by — events such as bump tests or calibrations, yellow alarms and red alerts.


Awareness of nearby devices

In the background, each device will keep track of other devices that are within 2 meters of it, and will flash and vibrate when a new device is added to the list. If the device no longer detects another device within 2 meters for a consistent 30 seconds, that device’s ID will disappear from the list. If that device reappears, both will receive the warning again, and the IDs will be added to each list. 

This ensures that devices will not go into alarm multiple times for the same nearby device, but also ensures that if two users keep coming in close contact after being separated, the device will keep notifying them of the social distance violation.

Each device can keep track of 30 other device IDs at a time. If additional devices are in close proximity, they will be ignored.


Limitations of close contact detection

Close contact detection between devices will not always be 100% accurate. In cases where devices are back to back, or where the environment reduces signal strength, devices may not trigger a warning even when they are in close proximity.


The close contact detection feature will be made available upon request. To learn more, contact our Customer Care team.