Do Not Disturb Broadcast

Idea: App to enable/disable Do Not Disturb mode on multiple devices when one device makes/receives a call.

Problem: Answer a call on one phone, then a call comes in on Skype (tablet) and then another call on another phone.

Initial thoughts

• How do we link devices?
• Should links be uni or bi-directional?
• Should a device broadcast a 'Do Not Disturb' signal and only linked devices respond (a bit like networking where NICs only care about packets destined for their address)? Privacy implications?
• Can we detect the start and end of any 'call' - including all the different apps, phone etc.?
• We need to 'revert' to the previous setting, so if a device was already in DND mode before the broadcast, it should be unchanged at the end of the call (i.e. always revert rather than toggle).
• Bluetooth or wifi for broadcast? Bluetooth works anywhere, but may require more permissions and can potentially be snooped on (or at least traffic analysis), plus not clear if you can pair multiple devices in a 'network'. Wifi probably works for most cases, and also allows for devices being in different rooms but still the same building - but how do you detect the devices on the network? MAC address?
• What level of security is required? Does it matter if other devices nearby see that a call is being made - the user can probably hear them anyway?
• Could KDE Connect handle this? Desktop is likely to be on whenever this functionality is required.