alt Hacker NewsI don't know how practical but I always thought of extending the Wifi protocol with a clock broadcast
That way all the microwaves of the world could listen in and update their clocks accordingly
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Nokia proposed using SIB9 5G time transmission as time syncing in clocks, the idea being that transmission is available openly even for non-subscriber. Softbank later proposed commercializing the service, which is unclear to me since surely the public transmission would be enough for casual users and anyone requiring more would already use full 5G to control the device anyway.
Why bloat Wi-Fi with a clock signal when we already have a perfectly cromulent network time protocol?
But how do you make it secure? Add a signature with a fixed key?
Consensus Time https://m.xkcd.com/2594/
Apparently at least Bluetooth has something called Current Time Service (CTS) (BLE GATT service 0x1805). If you pair a cheap "smartband" to a phone, it'll set itself, even without using any apps. Neat! I guess it uses CTS?