--- a/hal/Hal.cpp
+++ b/hal/Hal.cpp
@@ -845,53 +845,16 @@ NotifySwitchChange(const SwitchEvent& aE
   // first. We should check if this pointer is valid.
   if (!sSwitchObserverLists)
     return;
 
   SwitchObserverList& observer = GetSwitchObserverList(aEvent.device());
   observer.Broadcast(aEvent);
 }
 
-static AlarmObserver* sAlarmObserver;
-
-bool
-RegisterTheOneAlarmObserver(AlarmObserver* aObserver)
-{
-  MOZ_ASSERT(!InSandbox());
-  MOZ_ASSERT(!sAlarmObserver);
-
-  sAlarmObserver = aObserver;
-  RETURN_PROXY_IF_SANDBOXED(EnableAlarm(), false);
-}
-
-void
-UnregisterTheOneAlarmObserver()
-{
-  if (sAlarmObserver) {
-    sAlarmObserver = nullptr;
-    PROXY_IF_SANDBOXED(DisableAlarm());
-  }
-}
-
-void
-NotifyAlarmFired()
-{
-  if (sAlarmObserver) {
-    sAlarmObserver->Notify(void_t());
-  }
-}
-
-bool
-SetAlarm(int32_t aSeconds, int32_t aNanoseconds)
-{
-  // It's pointless to program an alarm nothing is going to observe ...
-  MOZ_ASSERT(sAlarmObserver);
-  RETURN_PROXY_IF_SANDBOXED(SetAlarm(aSeconds, aNanoseconds), false);
-}
-
 void
 SetProcessPriority(int aPid, ProcessPriority aPriority, uint32_t aLRU)
 {
   // n.b. The sandboxed implementation crashes; SetProcessPriority works only
   // from the main process.
   PROXY_IF_SANDBOXED(SetProcessPriority(aPid, aPriority, aLRU));
 }
 

--- a/hal/Hal.h
+++ b/hal/Hal.h
@@ -37,18 +37,16 @@ class nsPIDOMWindowInner;
 # define MOZ_HAL_NAMESPACE hal
 # define MOZ_DEFINED_HAL_NAMESPACE 1
 #endif
 
 namespace mozilla {
 
 namespace hal {
 
-typedef Observer<void_t> AlarmObserver;
-
 class WindowIdentifier;
 
 typedef Observer<int64_t> SystemClockChangeObserver;
 typedef Observer<SystemTimezoneChangeInformation> SystemTimezoneChangeObserver;
 
 } // namespace hal
 
 namespace MOZ_HAL_NAMESPACE {
@@ -428,51 +426,16 @@ hal::SwitchState GetCurrentSwitchState(h
 
 /**
  * Notify switch status change from input device.
  */
 void NotifySwitchStateFromInputDevice(hal::SwitchDevice aDevice,
                                       hal::SwitchState aState);
 
 /**
- * Register an observer that is notified when a programmed alarm
- * expires.
- *
- * Currently, there can only be 0 or 1 alarm observers.
- */
-MOZ_MUST_USE bool RegisterTheOneAlarmObserver(hal::AlarmObserver* aObserver);
-
-/**
- * Unregister the alarm observer.  Doing so will implicitly cancel any
- * programmed alarm.
- */
-void UnregisterTheOneAlarmObserver();
-
-/**
- * Notify that the programmed alarm has expired.
- *
- * This API is internal to hal; clients shouldn't call it directly.
- */
-void NotifyAlarmFired();
-
-/**
- * Program the real-time clock to expire at the time |aSeconds|,
- * |aNanoseconds|.  These specify a point in real time relative to the
- * UNIX epoch.  The alarm will fire at this time point even if the
- * real-time clock is changed; that is, this alarm respects changes to
- * the real-time clock.  Return true iff the alarm was programmed.
- *
- * The alarm can be reprogrammed at any time.
- *
- * This API is currently only allowed to be used from non-sandboxed
- * contexts.
- */
-MOZ_MUST_USE bool SetAlarm(int32_t aSeconds, int32_t aNanoseconds);
-
-/**
  * Set the priority of the given process.
  *
  * Exactly what this does will vary between platforms.  On *nix we might give
  * background processes higher nice values.  On other platforms, we might
  * ignore this call entirely.
  */
 void SetProcessPriority(int aPid,
                         hal::ProcessPriority aPriority,

--- a/hal/HalInternal.h
+++ b/hal/HalInternal.h
@@ -60,26 +60,16 @@ void DisableScreenConfigurationNotificat
 void EnableSwitchNotifications(hal::SwitchDevice aDevice);
 
 /**
  * Disable switch notifications from the backend
  */
 void DisableSwitchNotifications(hal::SwitchDevice aDevice);
 
 /**
- * Enable alarm notifications from the backend.
- */
-MOZ_MUST_USE bool EnableAlarm();
-
-/**
- * Disable alarm notifications from the backend.
- */
-void DisableAlarm();
-
-/**
  * Enable system clock change notifications from the backend.
  */
 void EnableSystemClockChangeNotifications();
 
 /**
  * Disable system clock change notifications from the backend.
  */
 void DisableSystemClockChangeNotifications();

deleted file mode 100644
--- a/hal/fallback/FallbackAlarm.cpp
+++ /dev/null
@@ -1,79 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this file,
- * You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include "Hal.h"
-
-#include <algorithm>
-
-#include "mozilla/ClearOnShutdown.h"
-#include "mozilla/StaticPtr.h"
-#include "nsComponentManagerUtils.h"
-#include "nsITimer.h"
-#include "nsThreadUtils.h"
-
-namespace mozilla {
-namespace hal_impl {
-
-static void
-TimerCallbackFunc(nsITimer *aTimer, void *aClosure)
-{
-  hal::NotifyAlarmFired();
-}
-
-static StaticRefPtr<nsITimer> sTimer;
-
-bool
-EnableAlarm()
-{
-  static bool initialized = false;
-  if (!initialized) {
-    initialized = true;
-    ClearOnShutdown(&sTimer);
-  }
-
-  nsCOMPtr<nsITimer> timer = do_CreateInstance("@mozilla.org/timer;1");
-  sTimer = timer;
-  MOZ_ASSERT(sTimer);
-  return true;
-}
-
-void
-DisableAlarm()
-{
-  /*
-   * DisableAlarm() may be called after sTimer has been set to null by
-   * ClearOnShutdown().
-   */
-  if (sTimer) {
-    sTimer->Cancel();
-  }
-}
-
-bool
-SetAlarm(int32_t aSeconds, int32_t aNanoseconds)
-{
-  if (!sTimer) {
-    MOZ_ASSERT(false, "We should have enabled the alarm");
-    return false;
-  }
-
-  // Do the math to convert aSeconds and aNanoseconds into milliseconds since
-  // the epoch.
-  int64_t milliseconds = static_cast<int64_t>(aSeconds) * 1000 +
-                         static_cast<int64_t>(aNanoseconds) / 1000000;
-
-  // nsITimer expects relative milliseconds.
-  int64_t relMilliseconds = milliseconds - PR_Now() / 1000;
-
-  // If the alarm time is in the past relative to PR_Now(),
-  // we choose to immediately fire the alarm. Passing 0 means nsITimer will
-  // queue a timeout event immediately.
-  sTimer->InitWithFuncCallback(TimerCallbackFunc, nullptr,
-                               clamped<int64_t>(relMilliseconds, 0, INT32_MAX),
-                               nsITimer::TYPE_ONE_SHOT);
-  return true;
-}
-
-} // namespace hal_impl
-} // namespace mozilla

--- a/hal/gonk/GonkHal.cpp
+++ b/hal/gonk/GonkHal.cpp
@@ -1110,96 +1110,16 @@ WaitForAlarm(void* aData)
       NS_DispatchToMainThread(event);
     }
   }
 
   pthread_cleanup_pop(1);
   return nullptr;
 }
 
-bool
-EnableAlarm()
-{
-  MOZ_ASSERT(!sAlarmData);
-
-  int alarmFd = open("/dev/alarm", O_RDWR);
-  if (alarmFd < 0) {
-    HAL_LOG("Failed to open alarm device: %s.", strerror(errno));
-    return false;
-  }
-
-  UniquePtr<AlarmData> alarmData = MakeUnique<AlarmData>(alarmFd);
-
-  struct sigaction actions;
-  memset(&actions, 0, sizeof(actions));
-  sigemptyset(&actions.sa_mask);
-  actions.sa_flags = 0;
-  actions.sa_handler = ShutDownAlarm;
-  if (sigaction(SIGUSR1, &actions, nullptr)) {
-    HAL_LOG("Failed to set SIGUSR1 signal for alarm-watcher thread.");
-    return false;
-  }
-
-  pthread_attr_t attr;
-  pthread_attr_init(&attr);
-  pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
-
-  int status = pthread_create(&sAlarmFireWatcherThread, &attr, WaitForAlarm,
-                              alarmData.get());
-  if (status) {
-    alarmData.reset();
-    HAL_LOG("Failed to create alarm-watcher thread. Status: %d.", status);
-    return false;
-  }
-
-  pthread_attr_destroy(&attr);
-
-  // The thread owns this now.  We only hold a pointer.
-  sAlarmData = alarmData.release();
-  return true;
-}
-
-void
-DisableAlarm()
-{
-  MOZ_ASSERT(sAlarmData);
-
-  // NB: this must happen-before the thread cancellation.
-  sAlarmData = nullptr;
-
-  // The cancel will interrupt the thread and destroy it, freeing the
-  // data pointed at by sAlarmData.
-  DebugOnly<int> err = pthread_kill(sAlarmFireWatcherThread, SIGUSR1);
-  MOZ_ASSERT(!err);
-}
-
-bool
-SetAlarm(int32_t aSeconds, int32_t aNanoseconds)
-{
-  if (!sAlarmData) {
-    HAL_LOG("We should have enabled the alarm.");
-    return false;
-  }
-
-  struct timespec ts;
-  ts.tv_sec = aSeconds;
-  ts.tv_nsec = aNanoseconds;
-
-  // Currently we only support RTC wakeup alarm type.
-  const int result = ioctl(sAlarmData->mFd,
-                           ANDROID_ALARM_SET(ANDROID_ALARM_RTC_WAKEUP), &ts);
-
-  if (result < 0) {
-    HAL_LOG("Unable to set alarm: %s.", strerror(errno));
-    return false;
-  }
-
-  return true;
-}
-
 static int
 OomAdjOfOomScoreAdj(int aOomScoreAdj)
 {
   // Convert OOM adjustment from the domain of /proc/<pid>/oom_score_adj
   // to the domain of /proc/<pid>/oom_adj.
 
   int adj;
 

--- a/hal/moz.build
+++ b/hal/moz.build
@@ -39,17 +39,16 @@ SOURCES += [
 ]
 
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'android':
     LOCAL_INCLUDES += [
         '/widget/android',
     ]
     UNIFIED_SOURCES += [
         'android/AndroidSensor.cpp',
-        'fallback/FallbackAlarm.cpp',
         'fallback/FallbackPower.cpp',
         'linux/LinuxMemory.cpp',
     ]
     # AndroidHal.cpp cannot be built in unified mode because it relies on HalImpl.h.
     SOURCES += [
         'android/AndroidHal.cpp',
     ]
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gonk':
@@ -67,73 +66,68 @@ elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'go
         'linux/LinuxPower.cpp',
     ]
     # GonkHal.cpp cannot be built in unified mode because it relies on HalImpl.h.
     SOURCES += [
         'gonk/GonkHal.cpp',
     ]
 elif CONFIG['OS_TARGET'] == 'Linux':
     UNIFIED_SOURCES += [
-        'fallback/FallbackAlarm.cpp',
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackSensor.cpp',
         'fallback/FallbackVibration.cpp',
         'linux/LinuxMemory.cpp',
         'linux/LinuxPower.cpp',
     ]
     if CONFIG['MOZ_ENABLE_DBUS']:
         UNIFIED_SOURCES += [
             'linux/UPowerClient.cpp',
         ]
     else:
         UNIFIED_SOURCES += [
             'fallback/FallbackBattery.cpp',
         ]
 elif CONFIG['OS_TARGET'] == 'WINNT':
     UNIFIED_SOURCES += [
-        'fallback/FallbackAlarm.cpp',
         'fallback/FallbackMemory.cpp',
         'fallback/FallbackPower.cpp',
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackVibration.cpp',
         'windows/WindowsSensor.cpp',
     ]
     # WindowsBattery.cpp cannot be built in unified mode because it relies on HalImpl.h.
     SOURCES += [
         'windows/WindowsBattery.cpp',
     ]
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'cocoa':
     UNIFIED_SOURCES += [
         'cocoa/CocoaBattery.cpp',
-        'fallback/FallbackAlarm.cpp',
         'fallback/FallbackMemory.cpp',
         'fallback/FallbackPower.cpp',
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackVibration.cpp',
     ]
 elif CONFIG['OS_TARGET'] in ('OpenBSD', 'NetBSD', 'FreeBSD', 'DragonFly'):
     UNIFIED_SOURCES += [
-        'fallback/FallbackAlarm.cpp',
         'fallback/FallbackMemory.cpp',
         'fallback/FallbackPower.cpp',
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackSensor.cpp',
         'fallback/FallbackVibration.cpp',
     ]
     if CONFIG['MOZ_ENABLE_DBUS']:
         UNIFIED_SOURCES += [
             'linux/UPowerClient.cpp',
         ]
     else:
         UNIFIED_SOURCES += [
             'fallback/FallbackBattery.cpp',
         ]
 else:
     UNIFIED_SOURCES += [
-        'fallback/FallbackAlarm.cpp',
         'fallback/FallbackBattery.cpp',
         'fallback/FallbackMemory.cpp',
         'fallback/FallbackPower.cpp',
         'fallback/FallbackScreenConfiguration.cpp',
         'fallback/FallbackSensor.cpp',
         'fallback/FallbackVibration.cpp',
     ]