Effects of Obstructions on the Accuracy of Bluetooth Contact Tracing

David Labrique1, an independent researcher, has a new paper on the Effects of Obstructions on the Accuracy of Bluetooth Contact Tracing.

Bluetooth Contact Tracing

He looks into the variation of Bluetooth received signal strength (RSSI) due to different types of obstruction such as walls and the human body. He explains how RSSI is being used in contact tracing apps and asks whether it’s possible to have false positives when there’s wall between smartphones or false negatives when people are close together but blocked by their bodies.

David used a Raspberry Pi as a Bluetooth emitter and a smartphone as a receiver, situated 1 metre apart and placed various obstacles between them. He found that drywall and stud walls were ineffective at reducing Bluetooth signal strength. Conversely, human bodies drastically reduce Bluetooth signals.

He concludes:

Smart watches might be possible candidates for more accurate contact tracing as they are less obstructed by the body when worn on the wrist

It’s well known that human bodies block Bluetooth. We have an article that explains how this phenomenon can even be used to infer direction.

What David didn’t do was test at different levels of power output. We assume he just used full power which will go through walls. Solutions such as our CATT use lower power predominantly to save battery life but also because there’s no need to transmit further. There’s are also factors at play in a smartphone app such as the variance of signal power across transmitting smartphone, the variance in the ability of different smartphones to receive the signal and the ability (or not) of smartphones to be able to transmit and receive in background when the app isn’t showing/running. These factors make app based contact tracing even more unreliable. Stand alone devices, such as smart watches mentioned by David, work better.

Read about CATT Social Distancing Solution

Social Distancing Beacons

Bluetooth Beacons getting COVID-19 Impacted Business Back on Track

It has been an enormously challenging time for so many organisations during the COVID-19 lockdown. Many are now scrambling to implement new measures within their business to help safeguard workers health and avoid further disruption and shutdowns.

With Governments worldwide issuing and updating guidance on a regular basis, many businesses are turning to technology experts for practical easy to implement solutions in the longer term fight against the virus.

In recent years, Bluetooth Beacon technologies have been gaining ground in many industries, with the global Beacon Technology market projected to reach USD 1249 million by 2026, at a CAGR of 25.8% during 2021-2026. The technology, in its simplicity, can be deployed in numerous and varied business applications, most recently in supporting social distancing and other compliance measures.

Here, we learn how Bluetooth Beacon technologies, such as BeaconZone CATT, are being deployed to safeguard the health and wellbeing of both employees and customers, and can help get your business back on track.

The Challenge


All employers have a duty of care to ensure their workplace is safe for workers to return to, by mitigating risks and implementing Government issued COVID-19 guidance.
Each business will encounter its own challenges in meeting both current requirements and potential needs for renewed restrictions and lockdowns, dependent on business environments, employee numbers, industry and activities. This requires, in many instances, huge shifts in business thinking, models and processes.

There is no doubt that being flexible and open to new ways of working will help make such changes more successful. As well as stringent cleaning and hygiene measures, social distancing is perhaps the biggest challenge, requiring behavioural as well as practical changes and consideration across all aspects of your business.

Installing screens and barriers to physically separate people has its merits but is not, in many circumstances practical, which is why many employers and organisations are turning to alert, track and trace technologies for help.

As well as the extensive guides provided by Government, The UK’s Chartered Institute of Personnel and Development (CPID) have several useful tools and detailed guidance to help support your returning to workplace needs.

Bluetooth Beacons to the Rescue

Bluetooth beacon technologies, already widely used in many business applications, from logistics and asset management to location-based gaming, marketing and events management, temperature and humidity monitoring and many more, are a game changer in supporting businesses in their fight against COVID-19, including:

  • Social Distancing:  Standalone social distancing devices and tracking systems,  such as BeaconZone CATT, provide an easy to implement and practical solution to help and remind your workers to retain social distancing with a range of wearables, including wristbands and lanyards that flash and vibrate when social distancing is infringed. Data collected and synced through management stations empower your managers to effectively monitor, report and resolve repeated infringements and manage and mitigate further risks and non-compliance.
  • Staff Locating:  Systems such as BeaconRTLS™, previously mainly used in factories and warehouses, are now being used more in COVID-19 Risk Assessments to determine the location of staff and occupancy of buildings. What might have seemed to be an invasion of privacy is now seen as something desirable to help ensure the safety of workers and audit compliance to government and industry-specific guidelines.
  • Lone Working: There has been an increase in the use of beacons providing touch-free ‘check-in’ for workers and for SOS. This includes use of gateways to automatically know when a worker has been at a specific locations, full locating systems and control centre systems such as TRBOnet. These systems allow a button to be pressed by the worker when, for example, there’s a medical emergency, threat to life or in customer facing scenarios, a potentially abusive situation. Such systems assist in complying with government lone worker regulations as well as provide peace of mind for both the employee as well as the employer.
  • Process Change:  As many businesses are reviewing and implementing new processes to safeguard the safety of their workers and customers, finding ways to make these more onerous tasks more efficient will be critical to business success. A great example is the huge challenges the hospitality industry is facing with cafes and restaurants increasingly adopting beacon technology to identify tables for use in app-based ordering of food.

Benefits of Beacons

Beacon CATT is a standalone Bluetooth solution which can be easily deployed and is scalable for your business. It has been designed to be a one-off investment and requires no additional hardware or WiFi, Ethernet or cellular connection. You can be assured that performance is reliable and data is secured within your own business with ongoing support and help form our expert advisors.

Our solutions are increasing in demand and helping organisations get back to business post COVID-19 lockdown, including:

  • Enhancing protection against COVID-19
  • Giving workers confidence in workplace safety
  • Restoring business productivity and continuity
  • Being agile to changing compliance needs
  • Reducing breaches and chance of shutdowns

Tasked with securing social distancing measures within your organisation? Learn more and try our Evaluation Starter Kit NOW!

Social Distance Wristbands Help Keep Sites Operating

As offices and sites re-open and people go back to work, it’s necessary to introduce social distancing measures in the workplace. We are hearing of factories being shut down after site-specific infection. Poor social distancing measures ultimately jeopardises the continuity of work in your organisation.

No matter what measures you put in place there will be some workers who flout the guidelines and others who are so engrossed in work that they forget about social distancing.

Social distance wristbands and lanyard wearable devices remind workers to maintain social distancing. Complete solutions allow close contact events to be taken off the distance wristband each day to audit compliance and if necessary, perform contact tracing.

Read about Social Distance Wristbands for Workplace Social Distancing and Contact Tracing

Restaurant of the Future

With restaurants and pubs here in the UK scrambling to reopen this weekend, they need to find ways to provide self-service and minimise contact with staff. It’s interesting to see what was considered a ‘future restaurant’ in 2014 makes much more sense today:

The concept restaurant at Eggcellent in Tokyo used iBeacons for the location aspects together with smartglasses, augmented reality and gesture interfaces. An Engadget article covered the restaurant in more detail.

Read about Using Beacons in Hospitality

Read about social distance wristbands

UK NHS Covid-19 Contact Tracking Source Code Available

The UK NHS has just released the Android and iOS source code for the UK NHS Covid-19 contact tracking app. This is the code used before the recent switch to the Google/Apple mechanism.

The iOS readme explains how it works:

Our unique identifier is also known as our service characteristic. In the Bluetooth spec, devices can broadcast the availability of services. Each service can have multiple characteristics. We use a characteristic to uniquely identify our service and distinguish from all other sorts of Bluetooth devices. For every device we find with a matching characteristic, we record an identifier for the device we saw, the timestamp, and the RSSI of the Bluetooth signal, which will allow a team later on to determine who was in close proximity to individuals infected with the novel coronavirus

Read about social distance bands

UK Moves to Google-Apple Social Distancing API

Just under a month ago we wrote about Bluetooth RSSI, Social Distancing and Contact Tracing and how the UK Government was going their own way:

Google and Apple have implemented a new API to allow contact tracing apps to work well on iOS and Android. Some Governments, such as ours in the UK, have currently gone their own way with apps that use existing APIs. Such aforementioned restrictions stop smartphones seeing each other thus severely reducing their effectiveness. The apps won’t work properly and will provide very limited benefit.

We are not surprised that Sky News is reporting that there has now been a U-turn.

To all governments trying to use the standard iOS and Android APIs to measure social distancing and perform contact tracing: You are wasting important time.

Read about Beacons for Workplace Social Distancing and Contact Tracing

How Social Distancing Wearables Work

We have had people ask how social distancing beacons such as distance bands differ to ordinary beacons. Normally, beacons send out (called advertising) Bluetooth signals that are received (called scanning) by apps on smartphones or Bluetooth gateways:

There’s no actual connection taking place. One side is repeatedly sending while the other is listening.

For social distancing, the beacons advertise AND scan:

Each beacon is repeatedly sending out an id and listening for others. Again, no connection takes place. When beacon receives scan data, it also sees the signal strength which can be used to infer the distance and hence whether the remote beacon is within the social distancing distance.

Beacons can store the id, signal strength and time. This can be extracted later via connection from another device such as a smartphone or gateway.

Read about Beacons for Workplace Social Distancing and Contact Tracing

Bluetooth Social Distancing Beacon in Stock

We now have the M52-ST social distancing beacon in stock.

The beacon led flashes when two people wearing this beacon come close to one another. Each beacon stores up to 34,304 close contacts that can be extracted using the supplied iOS and Android app.

The app also allows setting of the time two people have to be together, the alarm type (led and/or sound) and a whitelist of up to 45 devices. The transmit power and signal strength trigger value can also be changed to fine tune the trigger distance for different physical situations.

Also see our Social Distancing System if you need a complete system for tracking and tracing.

Bluetooth RSSI, Social Distancing and Contact Tracing

In a previous post we explained how the Received Signal Strength Indication (RSSI) can be used to infer distance. Contract tracing apps provided by governments and workplace social distancing solutions use the RSSI to detect close contact. This post explores some factors that affect how well such systems work.

With Bluetooth LE the sender repeatedly sends out a small amount of data, called advertising, that takes of the order of 1ms to send. The repeat time, called the advertising period, is typically every 100 milliseconds to 10 seconds depending on the application.

Battery power use over time showing the 1ms spikes

A 1ms transmission uses a lot of battery power so there’s a tradeoff between the advertising period and battery life.

The receiver listens, called scanning, for Bluetooth advertising. Again this is battery intensive so scanning devices typically only do so for a few seconds. If they need to listen for a long time then there’s a gap of a few seconds between successive scans.

It can be seen that because the sender isn’t always sending and the receiver isn’t always listening the two might not align to cause detection. The advertising period, the scanning time and the time between scans all combine to cause a tradeoff between battery life and the responsiveness of the detection. In extreme cases detection can take a very long time or not at all.

Applying this to iOS and Android, the mobile OS manufacturers have exercised some control over what’s possible with apps so as to protect battery life. iOS is the strictest and doesn’t allow apps to advertise unless they are in the foreground and shown on the screen. There is a trick to cause advertising to wake up an iOS app to advertise for a very short time. However, it leads to poor triggering performance and can affect battery life.

Android is more capable and up until recent versions of Android, apps could advertise and scan in foreground and background. More recently, Google has restricted background activity such that Bluetooth is only advertised for a short time after the app has closed. There’s an even larger limitation on Android in that some manufacturers kill apps that work in background.

All this isn’t good for contact tracing apps. As previously mentioned , Google and Apple have implemented a new API to allow contact tracing apps to work well on iOS and Android. Some Governments, such as ours in the UK, have currently gone their own way with apps that use existing APIs. Such aforementioned restrictions stop smartphones seeing each other thus severely reducing their effectiveness. The apps won’t work properly and will provide very limited benefit. It has even been suggested the system might even be dangerous as it might be provide a false sense of security. There is a report that early trials of the UK tracing app and privacy concerns have caused the UK government to re-think their approach and are investing in research into a second Google/Apple centric app in case there’s a need to quickly change direction.

For our workplace social distancing solution we have avoided use of apps for close-contact advertising and scanning. Instead we use smartband-like devices so that we are in full control of how and when the devices advertise and scan.

While wearable beacons only usually advertise, our custom firmware in social distancing wristbands performs both advertising and scanning so that devices can mutually detect one another. The heavy battery use means we still have to make a compromise between the responsiveness of triggering and battery use but at least it’s under our control rather than dictated by Google and Apple.

Contact Tracing Analysis

Following on from the previous post on Contract Tracing with Bluetooth and Google/Apple contact tracing, the BBC now has an interesting article on University of Oxford’s Big Data Institute analysis of use of contact tracing apps.

80% of smartphone owners would need to use the app with a absolute minimum of 56%. This is based on self-diagnosis rather than testing because:

“speed is of the essence”, and that delaying contact tracing by even a day from the onset of symptoms could make the difference between epidemic control and resurgence

We previously mentioned that the UK’s NHSX was going to use a contract tracing app written by VMWare and and University of Oxford’s Nuffield Department of Medicine. The latest BBC article tells us this was going to use GPS location readings and scanning QR codes. The Google/Apple contact tracing based on Bluetooth is going to be used instead so as to improve privacy and encourage greater take-up.

Read about our Social Distancing Solution (SDS)