  To address the massive spike in uncertainties triggered by the coronavirus
disease (COVID-19), 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. centralized or decentralized. 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
Apps vulnerabilities and the directions of research are identified, with a
special focus on the Bluetooth-inspired decentralized paradigm.
