diff --git a/examples/companion_radio/ui-new/UITask.cpp b/examples/companion_radio/ui-new/UITask.cpp
index b35c829d..5a3ed474 100644
--- a/examples/companion_radio/ui-new/UITask.cpp
+++ b/examples/companion_radio/ui-new/UITask.cpp
@@ -1694,7 +1694,7 @@ void UITask::begin(DisplayDriver* display, SensorManager* sensors, NodePrefs* no
   _sensors = sensors;
   _auto_off = millis() + AUTO_OFF_MILLIS;
 
-#if defined(PIN_USER_BTN) || defined(MECK_PMU_BUTTON)
+#if (defined(PIN_USER_BTN) || defined(MECK_PMU_BUTTON)) && !defined(MECK_DIAG_NO_PMU)
   user_btn.begin();
 #endif
 #if defined(PIN_USER_BTN_ANA)
@@ -2291,7 +2291,7 @@ void UITask::shutdown(bool restart){
 }
 
 bool UITask::isButtonPressed() const {
-#if defined(PIN_USER_BTN) || defined(MECK_PMU_BUTTON)
+#if (defined(PIN_USER_BTN) || defined(MECK_PMU_BUTTON)) && !defined(MECK_DIAG_NO_PMU)
   return user_btn.isPressed();
 #else
   return false;
@@ -2314,7 +2314,7 @@ void UITask::loop() {
     }
   }
 #endif
-#if defined(PIN_USER_BTN) || defined(MECK_PMU_BUTTON)
+#if (defined(PIN_USER_BTN) || defined(MECK_PMU_BUTTON)) && !defined(MECK_DIAG_NO_PMU)
   int ev = user_btn.check();
   if (ev == BUTTON_EVENT_CLICK) {
 #if defined(LilyGo_T5S3_EPaper_Pro)
diff --git a/variants/lilygo_twatch_s3/WatchChannelConfigScreen.h b/examples/companion_radio/ui-new/WatchChannelConfigScreen.h
similarity index 100%
rename from variants/lilygo_twatch_s3/WatchChannelConfigScreen.h
rename to examples/companion_radio/ui-new/WatchChannelConfigScreen.h
diff --git a/variants/lilygo_twatch_s3/TWatchS3Board.cpp b/variants/lilygo_twatch_s3/TWatchS3Board.cpp
index 3e947bee..82b0647d 100644
--- a/variants/lilygo_twatch_s3/TWatchS3Board.cpp
+++ b/variants/lilygo_twatch_s3/TWatchS3Board.cpp
@@ -177,11 +177,17 @@ bool TWatchS3Board::power_init() {
 
   PMU->disableIRQ(XPOWERS_AXP2101_ALL_IRQ);
   PMU->clearIrqStatus();
+#if !defined(MECK_DIAG_NO_PMU)
   // SHORT gives the click; NEGATIVE/POSITIVE are the press/release edges that
   // back PMUButton::isPressed().
   PMU->enableIRQ(XPOWERS_AXP2101_PKEY_SHORT_IRQ |
                  XPOWERS_AXP2101_PKEY_NEGATIVE_IRQ |
                  XPOWERS_AXP2101_PKEY_POSITIVE_IRQ);
+#endif
+  // TEMP DIAGNOSTIC (MECK_DIAG_NO_PMU, power bisect): with the PKEY IRQs left
+  // disabled above and PMUButton::check() skipped in UITask, the PMU-button
+  // subsystem is fully inert -- no IRQ config, no 30 ms polling, no dangling
+  // latch. disableIRQ(ALL)+clearIrqStatus above already left the PMU quiet.
 
   // 150 mA = 0.32C on the 470 mAh cell -- a modest bump over the 125 mA
   // vendor default (LilyGoWatchS3.cpp uses 125), well under the 0.5C rule.
diff --git a/variants/lilygo_twatch_s3/platformio.ini b/variants/lilygo_twatch_s3/platformio.ini
index 32d588c0..28bd989e 100644
--- a/variants/lilygo_twatch_s3/platformio.ini
+++ b/variants/lilygo_twatch_s3/platformio.ini
@@ -137,4 +137,42 @@ lib_deps =
   densaugeo/base64 @ ~1.4.0
 lib_ignore =
   AsyncTCP
-  ESPAsyncWebServer
\ No newline at end of file
+  ESPAsyncWebServer
+; ---------------------------------------------------------------------------
+; TEMP DIAGNOSTIC BUILD -- power-drain bisect (remove when concluded).
+; The S3 standalone firmware with the PMU-button subsystem fully disabled,
+; gated by MECK_DIAG_NO_PMU: the PKEY IRQ enable in power_init is skipped and
+; PMUButton::check()/begin()/isPressed() are compiled out of UITask, so there
+; is no IRQ config and no 30 ms I2C polling of the PMU (and no dangling latch).
+; Run the same wear test as the standalone S3 build; a materially slower drain
+; implicates the PMU-button subsystem in the S3-only excess. The PWR key does
+; nothing on this build (no click, no wake, no path-editor open) by design.
+; Revert: delete this env and grep MECK_DIAG_NO_PMU (one block in
+; TWatchS3Board.cpp, three in UITask.cpp).
+; Flash: pio run -e meck_twatch_s3_diag_nopmu -t upload
+; ---------------------------------------------------------------------------
+[env:meck_twatch_s3_diag_nopmu]
+extends = LilyGo_TWatchS3
+build_flags =
+  ${LilyGo_TWatchS3.build_flags}
+  -I examples/companion_radio/ui-new
+  -D MAX_CONTACTS=2000
+  -D MAX_GROUP_CHANNELS=40
+  -D OFFLINE_QUEUE_SIZE=1
+  -D ESP32_CPU_FREQ=80
+  -D MECK_DIAG_NO_PMU
+  -D FIRMWARE_VERSION='"Meck TWatch S3 DiagNoPMU v0.1"'
+build_src_filter = ${LilyGo_TWatchS3.build_src_filter}
+  +<helpers/esp32/*.cpp>
+  -<helpers/esp32/SerialBLEInterface.cpp>
+  +<helpers/ui/MomentaryButton.cpp>
+  +<../examples/companion_radio/*.cpp>
+  +<../examples/companion_radio/ui-new/*.cpp>
+  +<helpers/ui/LGFXDisplay.cpp>
+lib_deps =
+  ${LilyGo_TWatchS3.lib_deps}
+  densaugeo/base64 @ ~1.4.0
+lib_ignore =
+  AsyncTCP
+  ESPAsyncWebServer
+  ESP32 BLE Arduino
\ No newline at end of file