Table 1.

The technologies of the contact tracing apps and their salient features.

App information	App technology
	Bluetooth	DP-3Ta	GPS	PEPP-PTb	TCNc	Google and Apple	Others
Example countriesd	Australia; Singapore; Malaysia (MyTrace)	Austria; Finland; The Netherlands	Iceland (Ranking C-19); Italy (Diary); Jordan (Aman)	France; Georgia; Italy (Immuni)	Germany (ITO); Italy; The United States	Canada; Switzerland (SwissCovid); Germany (Corona-Warn-App)	New Zealand (digital diary); Australia, Canada, and New Zealand (GetHomeSafe); Malaysia (SELangkah)
Architecture	Centralized	Decentralized	Centralized	Centralized	Semicentralized	Decentralized	Centralized
Encounter handshake	Users exchange temporary IDs issued by the server	Unique 128-bit pseudorandom identifier by the server	Varies by implementation; some identify users by phone numbers	Users exchange temporary IDs issued by the server	TCN	Unique identifiers that are encrypted with a secret daily key held by the sending device	Real ID
Infection reporting	User-triggered upload	User-triggered upload, but the health authority never has access to contact log	User-triggered upload	User-triggered upload, but received massive privacy backlashes	The app notifies the user to potential infection	Not provisioned; delegated to app implementation	Varies by implementation; mostly user triggered
Privacy by design	No	Yes	No	No	Yes	Yes	No

^aDP-3T: Decentralized Privacy-Preserving Proximity Tracing.

^bPEPP-PT: Pan-European Privacy-Preserving Proximity Tracing.

^cTCN: Temporary Contact Numbers.

^dWhere there was more than one app used in a country, the name of the corresponding app is provided within parentheses.