diff --git a/fastpair/scanning/fastpair/fake_fast_pair_scanner.cc b/fastpair/scanning/fastpair/fake_fast_pair_scanner.cc
index 2f003064..1c5eae58 100644
--- a/fastpair/scanning/fastpair/fake_fast_pair_scanner.cc
+++ b/fastpair/scanning/fastpair/fake_fast_pair_scanner.cc
@@ -26,11 +26,11 @@ void FakeFastPairScanner::RemoveObserver(Observer* observer) {
 }
 
 void FakeFastPairScanner::NotifyDeviceFound(const BlePeripheral& peripheral) {
-  for (auto& obs : observer_) obs->OnDeviceFound(peripheral);
+  for (auto& obs : observer_.GetObservers()) obs->OnDeviceFound(peripheral);
 }
 
 void FakeFastPairScanner::NotifyDeviceLost(const BlePeripheral& peripheral) {
-  for (auto& obs : observer_) obs->OnDeviceLost(peripheral);
+  for (auto& obs : observer_.GetObservers()) obs->OnDeviceLost(peripheral);
 }
 
 }  // namespace fastpair
diff --git a/fastpair/scanning/fastpair/fast_pair_scanner_impl.cc b/fastpair/scanning/fastpair/fast_pair_scanner_impl.cc
index 6c36df43..4b4efc71 100644
--- a/fastpair/scanning/fastpair/fast_pair_scanner_impl.cc
+++ b/fastpair/scanning/fastpair/fast_pair_scanner_impl.cc
@@ -134,13 +134,13 @@ void FastPairScannerImpl::OnDeviceLost(const BlePeripheral& peripheral) {
                     << peripheral.GetName();
   device_address_advertisement_data_map_.erase(peripheral.GetName());
 
-  for (auto& observer : observer_) {
+  for (auto& observer : observer_.GetObservers()) {
     observer->OnDeviceLost(peripheral);
   }
 }
 
 void FastPairScannerImpl::NotifyDeviceFound(const BlePeripheral& peripheral) {
-  for (auto& observer : observer_) {
+  for (auto& observer : observer_.GetObservers()) {
     observer->OnDeviceFound(peripheral);
   }
 }
diff --git a/fastpair/scanning/mock_scanner_broker.h b/fastpair/scanning/mock_scanner_broker.h
index 59a44bef..0df0bea0 100644
--- a/fastpair/scanning/mock_scanner_broker.h
+++ b/fastpair/scanning/mock_scanner_broker.h
@@ -15,9 +15,9 @@
 #define THIRD_PARTY_NEARBY_FASTPAIR_SCANNING_MOCK_SCANNER_BROKER_H_
 
 #include "gmock/gmock.h"
+#include "fastpair/common/fast_pair_device.h"
 #include "fastpair/scanning/scanner_broker.h"
 #include "internal/base/observer_list.h"
-#include "fastpair/common/fast_pair_device.h"
 
 namespace nearby {
 namespace fastpair {
@@ -27,7 +27,6 @@ class MockScannerBroker : public ScannerBroker {
   MOCK_METHOD(void, StartScanning, (Protocol), (override));
   MOCK_METHOD(void, StopScanning, (Protocol), (override));
 
-
   void AddObserver(Observer* observer) override {
     observers_.AddObserver(observer);
   }
@@ -37,13 +36,13 @@ class MockScannerBroker : public ScannerBroker {
   }
 
   void NotifyDeviceFound(const FastPairDevice& device) {
-    for (auto& observer : observers_){
-       observer->OnDeviceFound(device);
+    for (auto& observer : observers_.GetObservers()) {
+      observer->OnDeviceFound(device);
     }
   }
 
-  void NotifyDeviceLost(const FastPairDevice& device)  {
-    for (auto& observer : observers_){
+  void NotifyDeviceLost(const FastPairDevice& device) {
+    for (auto& observer : observers_.GetObservers()) {
       observer->OnDeviceLost(device);
     }
   }
diff --git a/fastpair/scanning/scanner_broker_impl.cc b/fastpair/scanning/scanner_broker_impl.cc
index 3fd6ebf9..36a60d80 100644
--- a/fastpair/scanning/scanner_broker_impl.cc
+++ b/fastpair/scanning/scanner_broker_impl.cc
@@ -72,7 +72,7 @@ void ScannerBrokerImpl::StopFastPairScanning() {
 void ScannerBrokerImpl::NotifyDeviceFound(const FastPairDevice& device) {
   NEARBY_LOGS(INFO) << __func__ << ": Notifying device found, model id = "
                     << device.GetModelId();
-  for (auto& observer : observers_) {
+  for (auto& observer : observers_.GetObservers()) {
     observer->OnDeviceFound(device);
   }
 }
@@ -80,7 +80,7 @@ void ScannerBrokerImpl::NotifyDeviceFound(const FastPairDevice& device) {
 void ScannerBrokerImpl::NotifyDeviceLost(const FastPairDevice& device) {
   NEARBY_LOGS(INFO) << __func__ << ": Notifying device lost, model id = "
                     << device.GetModelId();
-  for (auto& observer : observers_) {
+  for (auto& observer : observers_.GetObservers()) {
     observer->OnDeviceLost(device);
   }
 }
diff --git a/fastpair/ui/fast_pair/fast_pair_notification_controller.cc b/fastpair/ui/fast_pair/fast_pair_notification_controller.cc
index b9851496..35f26de6 100644
--- a/fastpair/ui/fast_pair/fast_pair_notification_controller.cc
+++ b/fastpair/ui/fast_pair/fast_pair_notification_controller.cc
@@ -27,7 +27,7 @@ void FastPairNotificationController::RemoveObserver(Observer* observer) {
 
 void FastPairNotificationController::NotifyShowDiscovery(
     const DeviceMetadata& device) {
-  for (Observer* observer : observers_) {
+  for (Observer* observer : observers_.GetObservers()) {
     observer->OnUpdateDevice(device);
   }
 }
diff --git a/internal/base/BUILD b/internal/base/BUILD
index 998aec84..69faa567 100644
--- a/internal/base/BUILD
+++ b/internal/base/BUILD
@@ -17,6 +17,8 @@ cc_library(
         "//location/nearby/cpp/sharing:__subpackages__",
     ],
     deps = [
+        "//internal/platform:types",
+        "@com_google_absl//absl/base:core_headers",
         "@com_google_absl//absl/container:flat_hash_set",
     ],
 )
diff --git a/internal/base/observer_list.h b/internal/base/observer_list.h
index c3f45616..a4d44a2f 100644
--- a/internal/base/observer_list.h
+++ b/internal/base/observer_list.h
@@ -15,10 +15,9 @@
 #ifndef THIRD_PARTY_NEARBY_INTERNAL_BASE_OBSERVER_LIST_H_
 #define THIRD_PARTY_NEARBY_INTERNAL_BASE_OBSERVER_LIST_H_
 
-#include <string>
-#include <vector>
-
+#include "absl/base/thread_annotations.h"
 #include "absl/container/flat_hash_set.h"
+#include "internal/platform/mutex_lock.h"
 
 namespace nearby {
 
@@ -29,28 +28,45 @@ class ObserverList {
   using const_iterator =
       typename absl::flat_hash_set<ObserverType*>::const_iterator;
 
-  void AddObserver(ObserverType* observer) { observers_.emplace(observer); }
+  void AddObserver(ObserverType* observer) ABSL_LOCKS_EXCLUDED(mutex_) {
+    MutexLock lock(&mutex_);
+    observers_.insert(observer);
+  }
 
-  void RemoveObserver(ObserverType* observer) { observers_.erase(observer); }
+  void RemoveObserver(ObserverType* observer) ABSL_LOCKS_EXCLUDED(mutex_) {
+    MutexLock lock(&mutex_);
+    observers_.erase(observer);
+  }
 
-  bool HasObserver(ObserverType* observer) {
+  bool HasObserver(ObserverType* observer) ABSL_LOCKS_EXCLUDED(mutex_) {
+    MutexLock lock(&mutex_);
     return observers_.contains(observer);
   }
 
-  void Clear() { observers_.clear(); }
+  void Clear() ABSL_LOCKS_EXCLUDED(mutex_) {
+    MutexLock lock(&mutex_);
+    observers_.clear();
+  }
 
-  bool empty() const { return observers_.empty(); }
+  bool empty() const ABSL_LOCKS_EXCLUDED(mutex_) {
+    MutexLock lock(&mutex_);
+    return observers_.empty();
+  }
 
-  int size() const { return observers_.size(); }
+  int size() const ABSL_LOCKS_EXCLUDED(mutex_) {
+    MutexLock lock(&mutex_);
+    return observers_.size();
+  }
 
-  // Supports iterators
-  iterator begin() { return observers_.begin(); }
-  iterator end() { return observers_.end(); }
-  const_iterator begin() const { return observers_.begin(); }
-  const_iterator end() const { return observers_.end(); }
+  absl::flat_hash_set<ObserverType*> GetObservers()
+      ABSL_LOCKS_EXCLUDED(mutex_) {
+    MutexLock lock(&mutex_);
+    return observers_;
+  }
 
  private:
-  absl::flat_hash_set<ObserverType*> observers_;
+  mutable Mutex mutex_;
+  absl::flat_hash_set<ObserverType*> observers_ ABSL_GUARDED_BY(mutex_);
 };
 
 }  // namespace nearby
diff --git a/internal/platform/BUILD b/internal/platform/BUILD
index 368ce7d0..433aca27 100644
--- a/internal/platform/BUILD
+++ b/internal/platform/BUILD
@@ -340,6 +340,7 @@ cc_library(
     visibility = [
         "//connections:__subpackages__",
         "//fastpair:__subpackages__",
+        "//internal/base:__subpackages__",
         "//internal/flags:__subpackages__",
         "//internal/platform/implementation/windows:__subpackages__",
         "//internal/test:__subpackages__",
diff --git a/internal/platform/implementation/platform.h b/internal/platform/implementation/platform.h
index c26deb36..862bae8f 100644
--- a/internal/platform/implementation/platform.h
+++ b/internal/platform/implementation/platform.h
@@ -53,6 +53,10 @@
 #include "internal/platform/os_name.h"
 #include "internal/platform/payload_id.h"
 
+#ifdef CreateMutex
+#undef CreateMutex
+#endif
+
 namespace nearby {
 namespace api {
 
diff --git a/internal/platform/implementation/windows/mutex.h b/internal/platform/implementation/windows/mutex.h
index db30d65a..b9a908be 100644
--- a/internal/platform/implementation/windows/mutex.h
+++ b/internal/platform/implementation/windows/mutex.h
@@ -13,7 +13,6 @@
 // limitations under the License.
 #ifndef PLATFORM_IMPL_WINDOWS_MUTEX_H_
 #define PLATFORM_IMPL_WINDOWS_MUTEX_H_
-#include <windows.h>
 #include <stdio.h>
 #include <synchapi.h>
 
diff --git a/internal/platform/implementation/windows/platform.cc b/internal/platform/implementation/windows/platform.cc
index 10edeca1..70047776 100644
--- a/internal/platform/implementation/windows/platform.cc
+++ b/internal/platform/implementation/windows/platform.cc
@@ -65,6 +65,10 @@
 #include "internal/platform/implementation/windows/wifi_lan.h"
 #include "internal/platform/logging.h"
 
+#ifdef CreateMutex
+#undef CreateMutex
+#endif
+
 namespace nearby {
 namespace api {