The technology could help avert new surges in Covid-19 infections that might overwhelm hospitals battling an outbreak that has killed more than 350,000 people worldwide in just six months.
While many apps and related technologies are voluntary, other governments are enforcing their use, since health experts say at least 60 per cent of a population needs to activate them for contact tracing to be effective.
But privacy advocates warn they give unprecedented access to personal data that could be exploited by authorities or even third parties, despite pledges that information will be kept out of reach.
The stakes are high since only a small percentage of populations in many regions have been infected by the new coronavirus, meaning huge numbers of people are still at risk of infection.
Here is a rundown of the different approaches adopted since the first Covid-19 cases were reported in China last December, and what officials have learned from their experiences.
Asian countries were the first to roll out tracing apps, with China launching several that use either direct geolocalisation via cellphone networks, or data compiled from train and airline travel or highway checkpoints.
Their use was systematic and compulsory, and played a key role in allowing Beijing to lift regional lockdowns and halt contagions starting in April.
People are ranked green, yellow or red based on their travel history and exposure to infected people, to determine if they can travel or enter public areas.
South Korea, for its part, issued mass cellphone alerts announcing locations visited by infected patients, and ordered a tracking app installed on the phone of anyone ordered into isolation—aggressive measures that helped limit deaths to just a couple of hundred in a population of 51 million.
In Hong Kong and Taiwan, which have managed to limit deaths despite their proximity to China, officials use GPS and Wi-Fi to keep strict tabs on people in quarantine.
But most other countries turned to Bluetooth tracking via apps that remain voluntary and let authorities "see" when two people's devices come into close contact.
Officials say actual identities are encrypted, and anyone receiving an alert will not know who posed the potential contagion threat, but those pledges have failed to reassure many.
Australia's CovidSafe app, rolled out in April, has been downloaded 6.1 million times by its roughly 15 million smartphone users, though there is no data on how many remain active daily.
India's government launched the Aarogya Setu ("Bridge to Health") app, with more than 100 million downloads since April—less than one-tenth of its population, since only one in four Indians owns a smartphone.
In Iran, home to the deadliest outbreak in the Middle East, the Mask app is being pushed by officials, though rights groups say the government could be tempted by surveillance possibilities after months of unrest.
Pakistan, for its part, has tapped its powerful intelligence services to deploy secretive surveillance technology normally used to locate insurgents to track coronavirus patients and the people they come into contact with.