In response to the coronavirus disease (COVID-19) outbreak, there is an
ever-increasing number of national governments that are rolling out
contact-tracing Apps to aid the containment of the virus. The first hugely
contentious issue facing the Apps is the deployment framework, i.e. centralised
or decentralised. Based on this, the debate branches out to the corresponding
technologies that underpin these architectures, i.e. GPS, QR codes, and
Bluetooth. This work conducts a pioneering review of the above scenarios and
contributes a geolocation mapping of the current deployment. The
vulnerabilities and the directions of research are identified, with a special
focus on the Bluetooth-based decentralised scheme.