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.
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.
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.
Around the World, governments are advocating social distancing. Companies such as ourselves are offering tech-based solutions to warn about close contacts, as they happen. However, what is a safe distance?
Governments seem to recommend arbitrary distances, for example, China (1m), France (1m), Singapore (1m) through Australia (1.5m), Germany (1.5m), Greece (1.5m), Netherlands (1.5m) up to the United Kingdom (2m), Spain (2m) and Canada (2m). Countries are providing inconsistent guidelines. What do the various distances actually imply in terms of reducing the risk?
The risk of being infected is estimated to be 13% at less than 1m. Every extra metre of distance reduces the risk by half. 1m provides for a large reduction in infection but 2m is a much safer distance. 1.5m is a pragmatic option especially if other factors can be combined such as limiting the length of exposure, using of face protection or other contextual considerations. Neither distance, reducing length of exposure nor face masks provide complete protection from infection.
For tech based solutions it’s important to be able to fine tune the distance to governments’ advice and contextual considerations. It’s also important to be able to measure the length of exposure and filter out exposures that are so short as to pose negligible risk.
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.
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 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.
Here in the United Kingdom we have been locked down but we have been able to leave our homes to do essential work, shop, help sheltered people and take exercise. We have observed that companies still working through lockdown are not all practising social distancing. For example, in retail stores, employees regularly come close to one another either due to apathy, laziness or management pressure of productivity over safety. Workmen on the street can often be seen working close together.
As organisations come back to work there’s a greater awareness of workplace safety and unions are also taking a greater interest. Individuals need to know they are as safe as is practical. Governments are creating new working practice guidelines. For management, practising social distancing safety can actually be good for business. People are more willing to work, they feel the organisation has their interests in mind and ultimately there’s less risk of an outbreak on site causing worker absence and a potential site shutdown.
Governments producing guidelines and organisations implementing new working procedures don’t necessary produce changes in worker attitude, especially when it’s difficult to police the rules. This is where technology can help. A social distancing system can provide workers with warnings when they come too close and audit close contacts so that working patterns can be changed.
This isn’t about contact tracing that has been the contentious subject of recent news. While social distancing systems can produce contact tracing data, it’s unlikely to be useful in most businesses because close contact is always going to happen. Some governments realise this and guidelines stipulate extra measures when working within close contact, such as being mindful of the duration of the contact. Close contacts will happen in the workplace. It’s about reducing their number and duration.
Here are some factors to consider if you are seeking a social distancing system:
Cost – Consider the ongoing cost as well as the initial cost. Does the system unnecessarily use a software as a service (SAAS) model that ties you into monthly payments? Does it need a mobile wireless subscription for every user?
Setup – How easy is it to set up? For larger numbers of employees it’s important the tracking devices work ‘out of the box’. Lots of physical setup can also defeat the aim of reducing social and physical (screen) contact. Does the system require any site-wide infrastructure such as WiFi that’s almost certainly already unreliable due to congestion?
Scalability – How easy is it to scale to all your workforce? Where are the costs and technical bottlenecks?
Sync – How easy is it to sync? Again, data needs to be received from the tracking devices in a hands-off manner so as to reduce social and physical contact.
Data privacy – Where does the data end up? Remember your organisation might have data compliance requirements that require data be kept within the company or in a particular geographic region.
Output – What’s the output? It’s unlikely a vendor provided system will provide the exact reporting you require. Look for systems that allow you access to raw data for importing into Excel or other systems. Look for systems that automate reporting so as to reduce effort and physical (device screen) contact.
