diff --git a/internal/test/BUILD b/internal/test/BUILD
index e8c5bf70..e3227fe4 100644
--- a/internal/test/BUILD
+++ b/internal/test/BUILD
@@ -47,6 +47,7 @@ cc_library(
         "//internal/platform/implementation:types",
         "@com_google_absl//absl/base:core_headers",
         "@com_google_absl//absl/container:flat_hash_map",
+        "@com_google_absl//absl/functional:any_invocable",
         "@com_google_absl//absl/status",
         "@com_google_absl//absl/status:statusor",
         "@com_google_absl//absl/strings",
@@ -76,6 +77,7 @@ cc_test(
         ":test",
         "//internal/data:data_manager",
         "//internal/network:types",
+        "//internal/platform:types",
         "//internal/platform/implementation:types",
         "//internal/platform/implementation/g3",  # fixdeps: keep
         "@com_github_protobuf_matchers//protobuf-matchers",
diff --git a/internal/test/fake_clock.cc b/internal/test/fake_clock.cc
index 3f464ea6..f737d187 100644
--- a/internal/test/fake_clock.cc
+++ b/internal/test/fake_clock.cc
@@ -76,4 +76,9 @@ int FakeClock::GetObserversCount() {
   return observers_.size();
 }
 
+void FakeClock::Reset() {
+  absl::MutexLock lock(&mutex_);
+  return observers_.clear();
+}
+
 }  // namespace nearby
diff --git a/internal/test/fake_clock.h b/internal/test/fake_clock.h
index 8c077e18..5b7a9af8 100644
--- a/internal/test/fake_clock.h
+++ b/internal/test/fake_clock.h
@@ -45,6 +45,8 @@ class FakeClock : public Clock {
 
   int GetObserversCount() ABSL_LOCKS_EXCLUDED(mutex_);
 
+  void Reset() ABSL_LOCKS_EXCLUDED(mutex_);
+
  private:
   mutable absl::Mutex mutex_;
   absl::Time now_ ABSL_GUARDED_BY(mutex_);
diff --git a/internal/test/fake_clock_test.cc b/internal/test/fake_clock_test.cc
index d06966e6..0f57ce56 100644
--- a/internal/test/fake_clock_test.cc
+++ b/internal/test/fake_clock_test.cc
@@ -35,6 +35,18 @@ TEST(FakeClock, TestFastForward) {
   EXPECT_EQ(clock.GetObserversCount(), 0);
 }
 
+TEST(FakeClock, TestReset) {
+  FakeClock clock;
+  int count = 0;
+  auto observer = [&count]() { count++; };
+  clock.AddObserver("test", observer);
+  clock.FastForward(absl::Nanoseconds(1500));
+  EXPECT_EQ(count, 1);
+  EXPECT_EQ(clock.GetObserversCount(), 1);
+  clock.Reset();
+  EXPECT_EQ(clock.GetObserversCount(), 0);
+}
+
 TEST(FakeClock, TestObserver) {
   FakeClock clock;
   int count = 0;
diff --git a/internal/test/fake_timer.cc b/internal/test/fake_timer.cc
index 70929e41..08d47e8a 100644
--- a/internal/test/fake_timer.cc
+++ b/internal/test/fake_timer.cc
@@ -1,4 +1,4 @@
-// Copyright 2021 Google LLC
+// Copyright 2021-2023 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -18,82 +18,110 @@
 #include <string>
 #include <utility>
 
+#include "absl/functional/any_invocable.h"
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
+#include "internal/platform/logging.h"
+#include "internal/platform/mutex_lock.h"
 
 namespace nearby {
 
-FakeTimer::FakeTimer(FakeClock* clock) : clock_(clock) {
-  id_ = std::to_string(absl::ToUnixNanos(absl::Now()));
-  clock_->AddObserver(id_, [this]() { ClockUpdated(); });
-}
+FakeTimer::FakeTimer(FakeClock* clock) : clock_(clock) {}
 
-FakeTimer::~FakeTimer() { clock_->RemoveObserver(id_); }
+FakeTimer::~FakeTimer() { Stop(); }
 
 bool FakeTimer::Start(int delay, int period,
                       absl::AnyInvocable<void()> callback) {
-  if (is_started_ || delay < 0 || period < 0) {
-    return false;
-  }
-  delay_ = delay;
-  period_ = period;
-  callback_ = std::move(callback);
-  start_time_ = clock_->Now();
-  fired_count_ = 0;
-  is_started_ = true;
-
-  return true;
+  MutexLock lock(&mutex_);
+  return InternalStart(delay, period, std::move(callback));
 }
 
 bool FakeTimer::Stop() {
-  is_started_ = false;
-  return true;
+  MutexLock lock(&mutex_);
+  return InternalStop();
 }
 
-bool FakeTimer::IsRunning() { return is_started_; }
+bool FakeTimer::IsRunning() {
+  MutexLock lock(&mutex_);
+  return !timer_data_.id.empty();
+}
 
 void FakeTimer::ClockUpdated() {
-  if (!is_started_) {
+  MutexLock lock(&mutex_);
+  TimerData timer_data = timer_data_;
+  if (timer_data.id.empty()) {
     return;
   }
 
   absl::Time now = clock_->Now();
-  int64_t duration = absl::ToInt64Milliseconds(now - start_time_);
-  FakeClock* clock = clock_;
-  // The timer may be released during callback, save period and delay to avoid
-  // access exception.
-  int period = period_;
-  int delay = delay_;
-
-  if (duration >= delay_ && fired_count_ == 0) {
-    ++fired_count_;
-    if (callback_ != nullptr) {
-      callback_();
+  if (!timer_data.is_delay_called &&
+      timer_data.last_time == timer_data.create_time &&
+      timer_data.last_time + absl::Milliseconds(timer_data.delay) <= now) {
+    timer_data.callback();
+    if (timer_data.id == timer_data_.id) {
+      timer_data.is_delay_called = true;
+      timer_data.last_time =
+          timer_data.last_time + absl::Milliseconds(timer_data.delay);
+      timer_data_ = timer_data;
     }
   }
 
-  if (period == 0 || duration < delay ||
-      ((clock_ != nullptr) && (clock_ != clock))) {
+  if (timer_data.period == 0 || timer_data.id != timer_data_.id) {
+    // timer is changed during callback.
     return;
   }
 
-  int count = (duration - delay) / period;
-  int should_fire_count = count - fired_count_ + 1;
-  for (int i = 0; i < should_fire_count; ++i) {
-    ++fired_count_;
-    if (callback_ != nullptr) {
-      callback_();
+  timer_data_ = timer_data;
+  while (timer_data.last_time + absl::Milliseconds(timer_data.period) <= now) {
+    timer_data.callback();
+    if (timer_data.id == timer_data_.id) {
+      timer_data.last_time += absl::Milliseconds(timer_data.period);
+    } else {
+      return;
     }
   }
+
+  timer_data_ = timer_data;
 }
 
 bool FakeTimer::FireNow() {
-  if (IsRunning() && callback_) {
-    callback_();
+  if (IsRunning()) {
+    timer_data_.callback();
     return true;
   }
 
   return false;
 }
 
+bool FakeTimer::InternalStart(int delay, int period,
+                              absl::AnyInvocable<void()> callback) {
+  if (delay < 0 || period < 0 || callback == nullptr) {
+    return false;
+  }
+
+  if (!timer_data_.id.empty()) {
+    NEARBY_LOGS(ERROR) << __func__ << ": timer is already running";
+    return false;
+  }
+
+  timer_data_.id = std::to_string(absl::ToUnixNanos(absl::Now()));
+  timer_data_.delay = delay;
+  timer_data_.period = period;
+  callback_ = std::move(callback);
+  timer_data_.callback = [&]() { callback_(); };
+  timer_data_.create_time = clock_->Now();
+  timer_data_.last_time = timer_data_.create_time;
+  clock_->AddObserver(timer_data_.id, [this]() { ClockUpdated(); });
+  return true;
+}
+
+bool FakeTimer::InternalStop() {
+  if (timer_data_.id.empty()) {
+    return true;
+  }
+  clock_->RemoveObserver(timer_data_.id);
+  timer_data_ = {};
+  return true;
+}
+
 }  // namespace nearby
diff --git a/internal/test/fake_timer.h b/internal/test/fake_timer.h
index 24a7c15e..6f4e2e20 100644
--- a/internal/test/fake_timer.h
+++ b/internal/test/fake_timer.h
@@ -1,4 +1,4 @@
-// Copyright 2021 Google LLC
+// Copyright 2021-2023 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 
 #include <string>
 
+#include "internal/platform/mutex.h"
 #include "internal/platform/timer.h"
 #include "internal/test/fake_clock.h"
 
@@ -35,16 +36,25 @@ class FakeTimer : public Timer {
   bool FireNow() override;
 
  private:
-  void ClockUpdated();
+  struct TimerData {
+    std::string id;
+    int delay;
+    int period;
+    bool is_delay_called = false;
+    absl::Time create_time;
+    absl::Time last_time;
+    std::function<void()> callback;
+  };
 
-  std::string id_;
-  int delay_ = 0;
-  int period_ = 0;
-  int fired_count_ = 0;
-  absl::Time start_time_;
-  bool is_started_ = false;
-  absl::AnyInvocable<void()> callback_;
+  void ClockUpdated();
+  bool InternalStart(int delay, int period,
+                     absl::AnyInvocable<void()> callback);
+  bool InternalStop();
+
+  mutable RecursiveMutex mutex_;
   FakeClock* clock_ = nullptr;
+  TimerData timer_data_;
+  absl::AnyInvocable<void()> callback_ = nullptr;
 };
 
 }  // namespace nearby
diff --git a/internal/test/fake_timer_test.cc b/internal/test/fake_timer_test.cc
index 2bbb59b4..89a185b9 100644
--- a/internal/test/fake_timer_test.cc
+++ b/internal/test/fake_timer_test.cc
@@ -14,10 +14,11 @@
 
 #include "internal/test/fake_timer.h"
 
-#include "gmock/gmock.h"
-#include "protobuf-matchers/protocol-buffer-matchers.h"
 #include "gtest/gtest.h"
+#include "absl/time/clock.h"
 #include "absl/time/time.h"
+#include "internal/platform/logging.h"
+#include "internal/test/fake_task_runner.h"
 
 namespace nearby {
 namespace {
@@ -105,10 +106,10 @@ TEST(FakeTimer, TestTimerDestructor) {
   FakeClock clock;
   {
     FakeTimer timer(&clock);
-    EXPECT_EQ(clock.GetObserversCount(), 1);
     int count = 0;
     auto callback = [&count]() { ++count; };
     timer.Start(100, 0, callback);
+    EXPECT_EQ(clock.GetObserversCount(), 1);
     EXPECT_TRUE(timer.IsRunning());
     EXPECT_EQ(count, 0);
     EXPECT_TRUE(timer.Stop());
@@ -160,5 +161,25 @@ TEST(FakeTimer, StartTimerInTimerProc) {
   EXPECT_EQ(count, 2);
 }
 
+TEST(FakeTimer, WaitForRunningTask) {
+  bool finish = false;
+  FakeClock clock;
+  FakeTimer timer1(&clock);
+  FakeTaskRunner task_runner{&clock, 1};
+
+  timer1.Start(50, 0, [&]() {
+    absl::SleepFor(absl::Milliseconds(2000));
+    finish = true;
+  });
+
+  task_runner.PostTask([&]() {
+    absl::SleepFor(absl::Milliseconds(10));
+    timer1.Stop();
+    EXPECT_TRUE(finish);
+  });
+
+  clock.FastForward(absl::Milliseconds(50));
+}
+
 }  // namespace
 }  // namespace nearby