New Delhi, Dec 12 : The Google-Apple exposure notification system or ENS (earlier called contact tracing) is now helping public health authorities in more than 50 countries, states and regions in their efforts to control COVID-19. The two tech giants joined hands to first launch the exposure notifications system in May to provide the technical foundation on which public health authorities around the globe can build apps for contact tracing. The exposure notification app uses Bluetooth, which can be used to detect if two devices are near each other � without revealing where the devices are. This week, California became the latest US state to launch an app using the ENS. "Forty per cent of the population in the UK and 17 per cent of the population in Uruguay have downloaded the app. In the US, 20 percent of Colorado and 53 percent of Washington D.C. have enabled ENS," Google said in a statement on Friday. In September, the Prime Minister of Finland, Sanna Marin, received an exposure notification, and in November, the governor of Virginia, Ralph Northam, had been infected and used Exposure Notifications to alert staff members who may have been exposed. Research has revealed that exposure notifications can "save lives at all levels of uptake" and showed that a staff dedicated to working on contact tracing combined with 15 per cent of the population using exposure notifications could reduce infections by 15 percent and deaths by 11 per cent.  Exposure Notifications became available to public health agencies to build apps on both Android phones and iPhones. When an exposure is detected, public health authorities now have more flexibility in determining the level of risk associated with that exposure based on technical information from the API. "Bluetooth calibration values for hundreds of devices have been updated to improve the detection of nearby devices," Google had said earlier. The API now supports interoperability between countries, following feedback from governments that have launched Exposure Notification apps. /IANS