wwvbgps vs Wave Sync Watch

Emulates WWVB longwave time broadcast using DAC harmonics to produce a very weak signal at the carrier frequency of 60KHz. This allows a radio-controlled clock (e.g. many Casio watches), to receive the signal when placed near the speaker of the iOS device. There are other apps that do this but they don't seem to use the GPS time signal, instead relying on the system clock which will drift when it doesn't have internet for a long time (e.g. at sea) because iOS does not appear to use GPS time for system clock updates. This app specifically avoids using the system clock and prefers GPS time. To force using GPS, try it in Airplane mode, with all the radios off. Tested with Casio GW M5610U.

Wave Sync Watch helps synchronize compatible radio-controlled watches when tower reception is weak or unavailable. The app generates a precise audio signal through your device speaker. When the watch is placed directly against the speaker, some radio-controlled watches can pick up the near-field signal through their receiver coil and decode the time pattern. This is not a long-range radio transmitter. It is a close-contact speaker-based signal tool for watches that support standard radio time protocols. Features: - NTP-corrected live clock - Manual NTP sync - Automatic protocol selection by region - Support for WWVB, DCF77, JJY40, JJY60, MSF, and BPC - Standard and experimental output modes - Live envelope preview during broadcast - Real-time transmitted-data inspector - Physical checklist before starting transmission - Light and dark mode