Wake up device when other device is nearby?

One way you could achieve this is by using CoreLocation and the beacon region monitoring APIs.

Idea:
iPad subscribed to monitoring beacon, works in background.
iPhone comes into range, foreground, advertises as beacon, wakes up iPad.

You could then use technologies like MultipeerConnectivity or straight up BLE peripheral / central roles to exchange data.

Be aware of the new location requirements of this solution, beacon region monitoring I believe requires the new allow precise location authorization.

Thanks!
I found out that there is something new under iOS14 called "Nearby Interaction". But both devices don't hold the connection it seems.