Table 1.

Simulated proximity detection methods and their possible realization with widespread sensors for personal devices.

Proximity detection range	Possible technological realization with personal devices	Exemplary studies or initiatives
0.2 m	Near field communication protocol11	Prior literature12, no country deployed as of today
1 m	Radio-frequency identification techniques13	Prior literature8, hospital study in Singapore14
	Bluetooth class 315	-
2 m	Bluetooth Low Energy (varying statements in literature, around 2 meters16, 17 to up to 10 meters6)	CT solutions based on the interface provided by Apple and Google18, for example, the Corona-Warn-App from Germany
10 m	Bluetooth class 215	Prior literature19
	GPS20	HaMagen (Israel), Private Kit (USA)4
Sites-wide	QR Codes21	Prior literature21, ZeroBase (USA)4, Luca (Germany), CT solutions in China, England and Wales22