# Contact Tracing: Ensuring Privacy and Security
## 2 Digital Contact Tracing: What Is Missing?
This observation is troublesome considering that there are guidelines and frameworks for many other applications to ensure that those apps are safe to use, but this is lacking for digital contact tracing. In essence, what framework should app developers, governments, and healthcare providers follow when deploying a digital contact tracing system? It is worth emphasising that decentralised contact tracing apps have inherent privacy limitations [11]. It is worth noting \"the Google Play Services component of these apps is problematic from a privacy viewpoint\" [12] (i.e., mainly for GAEN-based contact tracing apps users on Android). This may justify why many people are reluctant to download and use contact tracing apps (i.e., The health-privacy trade-off [13]). Known as test, trace, isolate, and quarantine (TTIQ), this strategy isolates only at-risk patients, instead of the entire population. This approach requires finding cases early, which, in the case of COVID-19, is difficult, as discussed earlier. Contact tracers in this situation require help to identify possible cases. Fuelled by the initial success that China, South Korea, and Singapore had with contact tracing [14], dozens of nations are now considering digital contact tracing solutions to identify cases quickly because \"app-based tracing remains more effective than conventional contact tracing\" [15]. Contact tracing consists of two components or systems: an epidemiological component, which is not the scope of this project, and a technical component [16]. Both have to work together for the systems to be effective [17]. Since smartphone penetration reaches 80% in the European Union [18], most attention concerning the technical component goes to smartphones. Contract tracing applications are mostly using four technologies or sensors on smartphones [5]:  
1. Cell. Using the mobile operators cell tower information. Crude, but simple;
2. Wi-Fi. Scan for nearby devices connected to the same Wi-Fi network;GPS. Using GPS and other positional data. However, these data, too, are relatively crude [19], especially in urban areas;
4. Bluetooth. Bluetooth beacons allow for short range transmission and reception and includes signal strength--specifically Bluetooth low energy (BLE). Discussing what technology to use goes hand in hand with the question: does that technology help curb the infection, and find the effective growth rate \(R_{e}\leq 1\)? Research shows that it does if adoption exceeds 6% [7]. However, even if user adoption is significantly lower, digital contact tracing applications can have a significant contribution to stop epidemic growth--especially when combined with other measures [7; 15; 16]. However, speed is of the essence: the time between detection of a case and notification of contacts must be as quick as possible: \"Combining traditional and digital contact tracing may leverage the advantages, and mitigate the limitations, of each approach\" [17]. Given these requirements, BLE proved the best sensor to estimate the relative distance between two people--even though BLE suffers from false positives [5]. However, recording proximity between different people inherently leads to privacy and security questions [17].