We have recently released a new halt data collection feature. Using this feature, a researcher can unregister a phone from inside the web interface on studies.beiwe.org, and that will block the participant’s phone from uploading any further data.
The phone might continue to collect data if the participant hasn’t uninstalled the app, but it would just sit on the phone in an encrypted state, and it wouldn’t be possible for the participant or anyone who obtains the participant’s phone to decrypt it. Once the participant uninstalls the app, all data collected by the app that’s still on the phone will be automatically deleted.