We are currently evaluating the possibility to port our Android app “SoniControl” to iOS. SoniControl is an ultrasonic firewall. It records audio in the background and looks for ultrasonic messages (e.g. Google Nearby messages) in the audio signal in the frequency range from 17-22kHz. Frequencies below 17kHz are removed by a bandpass filter. In case a message is detected, the app offers the user the option to block it. The main goal is to raise awareness and inform users about apps that use “data-over-sound” technologies like Google Nearby or Lisnr. These technologies use the microphone and loudspeaker of a smartphone to receive or send data over audio. Our current users let the app run in the background all day long, we show a notification in the status bar to remind them that it is running and is using battery (on iOS the status bar would turni red as when you use the Voice Memo app in the background).
Before implementing the firewall for iOS we want to ask the following questions:
- Is background audio processing as we need it a valid use case for the Audio Background Mode?
- Would we get the necessary permissions for an iOS version of SoniControl (i.e. start capturing audio in the foreground, keep doing it in the background, searching for anomalies, with the status bar turning red)?
- What are your thoughts on our use case?
Here is what I found so far:
- Current documentation on background modes (does not specify which use cases are allowed or not): https://developer.apple.com/documentation/bundleresources/information_property_list/uibackgroundmodes
- Review guidelines (do not specify which use cases are allowed or not): https://developer.apple.com/app-store/review/guidelines/
- It is hard to find up to date documentation on background audio: everyone seems to link to documentation that is not available anymore
- In this archive, (audio) “recording apps” seems to be a valid use case for the audio background mode.
- In this archive, the audio background mode is described as:
- “The app plays audible content in the background.”
Many people contacted us in the past and asked if an iOS version of SoniControl is available. There seem to be a large demand from the iOS user community and we hope that we can soon provide them with a solution.