Herald 2.2.0

Herald 2.2.0

Maintained by Adam Fowler, Adam Fowler.

Herald 2.2.0

  • By
  • adamfowleruk



Continuous proximity detection across iOS and Android devices in background mode for contact tracing and infection control according to epidemiology requirements.

All files are copyright 2020-2021 Herald Project Contributors and are provided under the Apache 2.0 license.

License: Apache-2.0

See LICENSE.txt and NOTICE.txt for details.




This solution will:

  • Operate on 98.0% of UK phones and 97.5% of phones worldwide without requiring a software update.
  • Detect 100% of iOS and Android devices within 8 metres for contact tracing.
  • Measure distance between devices at least once every 30 seconds for infection risk estimation.

This is a new, original, free and open source cross-platform proximity detection solution that has been developed according to epidemiology requirements (Ferretti, et al., 2020) for controlling COVID-19. This Bluetooth Low Energy (BLE) based solution offers accurate and frequent distance measurements between phones running iOS 9.3+ and Android 5.0+, including devices that do not support BLE advertising (circa 35% in the UK).

Key features

  • Works on the vast majority of phones in the UK (98.0%) and worldwide (97.5%) by minimising operating system and hardware requirements (Statcounter, 2020).
  • Fully operational as a background app on both iOS and Android devices for consistent and continuous use to maximise disease transmission monitoring and control across the population.
  • Low power usage (circa 2% per hour) to maximise population acceptance for continuous use.
  • Detection and identification of iOS and Android devices in both foreground and background modes is 100% to maximise contact tracing coverage.
  • One or more distance measurement per 30 second window for devices within epidemiologically relevant range (8 metres) for accurate infection risk estimation and case isolation; coverage is > 99.5% of 30 second windows for 2 to 3 devices, and 93% - 96% of windows for 9 to 10 devices.
  • RSSI measurements for distance estimation is 98.5% accurate within epidemiologically relevant range (8 metres).
  • Device identification payload agnostic to support both centralised, and decentralised approaches, as well as retrospective integration into existing solutions.
    • Transmit and receive for Herald Protocol based payloads
    • Transmit and receive for BlueTrace payloads
    • Receive for GAEN payloads
  • Apache-2.0 licensed and open source for ease of integration, reuse and transparency.

Hardware requirements

  • Operating system

    • iOS 9.3+, tested up to iOS 14.6.
    • Android 5.0+, tested up to Android 10.0 (API level 29).
  • Hardware

    • Apple iPhone 4S+, tested up to iPhone 11 Pro.
    • Android phones with BLE, including phones that do not support BLE advertising (circa 35% in UK).

Quick start

Please see the developer guide for how to integrate your app to Herald.

Test results

For current and historic test and efficacy results please see the Efficacy section of the Herald website.


Ferretti, L., Wymant, C., Kendall, M., Zhao, L., Nurtay, A., Abeler-Dörner, L., Parker, M., Bonsall, D., and Fraser, C. (2020) "Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing", Science, vol. 368, no. 6491, New York.

Statcounter 2020, Mobile Operating System Market Share, Statcounter Global Stats, viewed August 2020, https://gs.statcounter.com/os-market-share/mobile/worldwide