diff --git a/zephcore/CMakeLists.txt b/zephcore/CMakeLists.txt
index 6d5f9d5..13234b0 100644
--- a/zephcore/CMakeLists.txt
+++ b/zephcore/CMakeLists.txt
@@ -430,6 +430,7 @@ target_sources(app PRIVATE
   adapters/sensors/ZephyrEnvSensors.cpp
   helpers/AdvertDataHelpers.cpp
   helpers/oled_power.c
+  helpers/time_sync.c
 )
 
 # ========== Radio Driver Selection ==========
diff --git a/zephcore/app/CompanionMesh.cpp b/zephcore/app/CompanionMesh.cpp
index ccf8fc8..d40f3ee 100644
--- a/zephcore/app/CompanionMesh.cpp
+++ b/zephcore/app/CompanionMesh.cpp
@@ -16,6 +16,8 @@
 #include <ZephyrSensorManager.h>
 #include <adapters/sensors/SimpleLPP.h>
 #include <adapters/ble/ZephyrBLE.h>
+#include <adapters/gps/ZephyrGPSManager.h>
+#include <helpers/time_sync.h>
 #if IS_ENABLED(CONFIG_ZEPHCORE_UI_DESIGN_BUTTON) || IS_ENABLED(CONFIG_ZEPHCORE_UI_DESIGN_JOYSTICK)
 #include <ui_task.h>
 #define ZEPHCORE_HAS_UI_TASK 1
@@ -2239,6 +2241,7 @@ bool CompanionMesh::handleProtocolFrame(const uint8_t *data, size_t len)
 			// Arduino: only allow setting time forward (prevents time attacks)
 			if (secs >= curr) {
 				getRTCClock()->setCurrentTime(secs);
+				time_sync_report(TIME_SYNC_APP);
 				sendPacketOk();
 			} else {
 				sendPacketError(ERR_ILLEGAL_ARG);
diff --git a/zephcore/app/RepeaterMesh.cpp b/zephcore/app/RepeaterMesh.cpp
index 3fd3ed2..f0b8c25 100644
--- a/zephcore/app/RepeaterMesh.cpp
+++ b/zephcore/app/RepeaterMesh.cpp
@@ -11,6 +11,7 @@
 #include <adapters/sensors/SimpleLPP.h>
 #include <adapters/sensors/ZephyrEnvSensors.h>
 #include <adapters/gps/ZephyrGPSManager.h>
+#include <helpers/time_sync.h>
 #include <zephyr/kernel.h>
 #include <zephyr/device.h>
 #include <zephyr/devicetree.h>
@@ -53,6 +54,7 @@ static void uplink_time_sync_cb(uint32_t unix_ts)
 {
 	if (s_uplink_mesh) {
 		s_uplink_mesh->getRTCClock()->setCurrentTime(unix_ts);
+		time_sync_report(TIME_SYNC_WIFI);
 	}
 }
 #endif
diff --git a/zephcore/app/main_observer.cpp b/zephcore/app/main_observer.cpp
index 2f78646..e4b6a5f 100644
--- a/zephcore/app/main_observer.cpp
+++ b/zephcore/app/main_observer.cpp
@@ -17,7 +17,7 @@
 #include <zephyr/kernel.h>
 #include <zephyr/drivers/uart.h>
 #include <zephyr/sys/ring_buffer.h>
-#include <zephyr/logging/log.h>
+#include <helpers/time_sync.h>
 
 #define CLI_REPLY_SIZE 256
 
@@ -222,6 +222,7 @@ static mesh::ZephyrRTCClock s_rtc_clock;
 static void time_sync_cb(uint32_t unix_ts)
 {
 	s_rtc_clock.setCurrentTime(unix_ts);
+	time_sync_report(TIME_SYNC_WIFI);
 	LOG_INF("RTC synced from SNTP: %u", unix_ts);
 }
 
diff --git a/zephcore/helpers/CommonCLI.cpp b/zephcore/helpers/CommonCLI.cpp
index 9fcccc4..03fef0d 100644
--- a/zephcore/helpers/CommonCLI.cpp
+++ b/zephcore/helpers/CommonCLI.cpp
@@ -4,6 +4,7 @@
  */
 
 #include "CommonCLI.h"
+#include <helpers/time_sync.h>
 #include <helpers/TxtDataHelpers.h>
 #include <helpers/AdvertDataHelpers.h>
 #include <adapters/board/ZephyrBoard.h>
@@ -327,6 +328,7 @@ void CommonCLI::handleCommand(uint32_t sender_timestamp, const char* command, ch
         uint32_t curr = getRTCClock()->getCurrentTime();
         if (sender_timestamp > curr) {
             getRTCClock()->setCurrentTime(sender_timestamp + 1);
+            time_sync_report(TIME_SYNC_CLI);
             uint32_t now = getRTCClock()->getCurrentTime();
             time_t t = (time_t)now;
             struct tm *tm = gmtime(&t);
@@ -346,6 +348,7 @@ void CommonCLI::handleCommand(uint32_t sender_timestamp, const char* command, ch
         uint32_t curr = getRTCClock()->getCurrentTime();
         if (secs > curr) {
             getRTCClock()->setCurrentTime(secs);
+            time_sync_report(TIME_SYNC_CLI);
             time_t t = (time_t)secs;
             struct tm *tm = gmtime(&t);
             snprintf(reply, CLI_REPLY_SIZE, "OK - clock set: %02d:%02d - %d/%d/%d UTC",
diff --git a/zephcore/helpers/time_sync.c b/zephcore/helpers/time_sync.c
new file mode 100644
index 0000000..a503e89
--- /dev/null
+++ b/zephcore/helpers/time_sync.c
@@ -0,0 +1,45 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "time_sync.h"
+#include <adapters/gps/ZephyrGPSManager.h>
+#include <stdio.h>
+
+static enum time_sync_source s_last = TIME_SYNC_NONE;
+
+static const char *source_short_name(enum time_sync_source src)
+{
+	switch (src) {
+	case TIME_SYNC_GPS:  return "GPS";
+	case TIME_SYNC_APP:  return "App";
+	case TIME_SYNC_WIFI: return "WiFi";
+	case TIME_SYNC_CLI:  return "CLI";
+	default:             return NULL;
+	}
+}
+
+void time_sync_report(enum time_sync_source src)
+{
+	s_last = src;
+}
+
+const char *time_sync_display_label(void)
+{
+	if (gps_has_time_sync()) {
+		return "GPS";
+	}
+
+	const char *src = source_short_name(s_last);
+	if (!src) {
+		return "None";
+	}
+
+	if (s_last != TIME_SYNC_GPS) {
+		return src;
+	}
+
+	static char label[20];
+	snprintf(label, sizeof(label), "Local (%s)", src);
+	return label;
+}
diff --git a/zephcore/helpers/time_sync.h b/zephcore/helpers/time_sync.h
new file mode 100644
index 0000000..86c1719
--- /dev/null
+++ b/zephcore/helpers/time_sync.h
@@ -0,0 +1,28 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Track which source last set the RTC for UI display.
+ */
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+enum time_sync_source {
+	TIME_SYNC_NONE = 0,
+	TIME_SYNC_GPS,
+	TIME_SYNC_APP,
+	TIME_SYNC_WIFI,
+	TIME_SYNC_CLI,
+};
+
+/** Record a successful RTC set from @p src. */
+void time_sync_report(enum time_sync_source src);
+
+/** Label for System > Info > Time. GPS authority wins while gps_has_time_sync(). */
+const char *time_sync_display_label(void);
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/zephcore/helpers/ui-joystick/screens/system.cpp b/zephcore/helpers/ui-joystick/screens/system.cpp
index 457b34b..4ccd44a 100644
--- a/zephcore/helpers/ui-joystick/screens/system.cpp
+++ b/zephcore/helpers/ui-joystick/screens/system.cpp
@@ -8,6 +8,7 @@
 #include "../joystick_ui_task.h"
 #include "screen_helpers.h"
 #include <adapters/gps/ZephyrGPSManager.h>
+#include <helpers/time_sync.h>
 #include <helpers/ui/ui_mesh_actions.h>
 #include <zephyr/kernel.h>
 #include <zephyr/random/random.h>
@@ -303,7 +304,7 @@ int SystemTimeScreen::render(JoystickDisplay &display)
 
 	const char *labels[4] = { "Time:", "Date:", "TZ:", "Source:" };
 	const char *values[4] = { timeText, dateText, "UTC",
-							   _task->getGPSState() ? "GPS" : "App" };
+							   time_sync_display_label() };
 	int y = kContentY + 2;
 	for (int i = 0; i < 4; i++) {
 		display.setColor(JoystickDisplay::GREEN);
diff --git a/zephcore/src/main_companion.cpp b/zephcore/src/main_companion.cpp
index d056a6e..dcb16e7 100644
--- a/zephcore/src/main_companion.cpp
+++ b/zephcore/src/main_companion.cpp
@@ -23,6 +23,7 @@ LOG_MODULE_REGISTER(zephcore_main, CONFIG_ZEPHCORE_MAIN_LOG_LEVEL);
 #include <zephyr/bluetooth/bluetooth.h>
 #include <zephyr/drivers/hwinfo.h>
 #include <ZephyrSensorManager.h>
+#include <helpers/time_sync.h>
 #include "ui_task.h"
 #include "ui_mesh_actions.h"
 #include "oled_power.h"
@@ -461,6 +462,7 @@ static void gps_fix_callback(double lat, double lon, int64_t utc_time)
 	if (utc_time > 0) {
 		LOG_INF("GPS fix: RTC sync time=%lld", utc_time);
 		rtc_clock.setCurrentTime((uint32_t)utc_time);
+		time_sync_report(TIME_SYNC_GPS);
 	}
 
 #ifdef ZEPHCORE_LORA
diff --git a/zephcore/src/main_repeater.cpp b/zephcore/src/main_repeater.cpp
index a1a55b0..64f1500 100644
--- a/zephcore/src/main_repeater.cpp
+++ b/zephcore/src/main_repeater.cpp
@@ -41,6 +41,7 @@ extern "C" void bt_ctlr_assert_handle(char *file, uint32_t line)
 #include <app/RepeaterDataStore.h>
 #include <app/RepeaterMesh.h>
 #include <adapters/clock/ZephyrRTCClock.h>
+#include <helpers/time_sync.h>
 #include <ZephyrSensorManager.h>
 
 /* UI subsystem (display, buttons, buzzer) */
@@ -261,6 +262,7 @@ static void gps_fix_callback(double lat, double lon, int64_t utc_time)
 	if (utc_time > 0) {
 		LOG_INF("GPS fix: RTC sync time=%lld", utc_time);
 		rtc_clock.setCurrentTime((uint32_t)utc_time);
+		time_sync_report(TIME_SYNC_GPS);
 	}
 
 	int lat_deg = (int)lat;