diff --git a/presence/fpp/BUILD b/presence/fpp/BUILD
index f551c07b..2f12acb7 100644
--- a/presence/fpp/BUILD
+++ b/presence/fpp/BUILD
@@ -40,6 +40,7 @@ cc_test(
     srcs = ["fpp_manager_test.cc"],
     deps = [
         ":fpp_manager",
+        "//presence/implementation:sensor_fusion",
         "@com_github_protobuf_matchers//protobuf-matchers",
         "@com_google_absl//absl/status",
         "@com_google_googletest//:gtest_main",
diff --git a/presence/fpp/fpp_manager.cc b/presence/fpp/fpp_manager.cc
index a70265a4..f0ce1ec2 100644
--- a/presence/fpp/fpp_manager.cc
+++ b/presence/fpp/fpp_manager.cc
@@ -17,10 +17,12 @@
 #include <cstdint>
 #include <optional>
 #include <string>
+#include <utility>
 
 #include "absl/status/status.h"
 #include "internal/platform/logging.h"
 #include "presence/fpp/fpp_c_ffi/include/presence_detector.h"
+#include "presence/implementation/sensor_fusion.h"
 #include "presence/presence_zone.h"
 
 namespace nearby {
@@ -110,7 +112,7 @@ absl::Status FppManager::UpdateBleScanResult(uint64_t device_id,
 
 void FppManager::RegisterZoneTransitionListener(
     uint64_t callback_id, ZoneTransitionCallback callback) {
-  zone_transition_callbacks_[callback_id] = callback;
+  zone_transition_callbacks_[callback_id] = std::move(callback);
 }
 
 void FppManager::UnregisterZoneTransitionListener(uint64_t callback_id) {
@@ -147,9 +149,10 @@ void FppManager::CheckPresenceZoneChanged(uint64_t device_id,
     NEARBY_LOG(WARNING,
                "Updating zone transition callbacks with new zone. Zone=%p",
                new_estimate.proximity_state);
-    for (const auto& pair : zone_transition_callbacks_) {
-      pair.second(device_id, ConvertProximityStateToRangeType(
-                                 new_estimate.proximity_state));
+    for (auto& pair : zone_transition_callbacks_) {
+      pair.second.on_proximity_zone_changed(
+          device_id,
+          ConvertProximityStateToRangeType(new_estimate.proximity_state));
     }
   }
 }
diff --git a/presence/fpp/fpp_manager.h b/presence/fpp/fpp_manager.h
index 50b616af..d13e4adb 100644
--- a/presence/fpp/fpp_manager.h
+++ b/presence/fpp/fpp_manager.h
@@ -31,7 +31,6 @@ namespace presence {
 // between fpp and NP sensor fusion
 class FppManager {
  public:
-  using ZoneTransitionCallback = SensorFusion::ZoneTransitionCallback;
   using RangeType = PresenceZone::DistanceBoundary::RangeType;
 
   FppManager() { presence_detector_handle_ = presence_detector_create(); }
diff --git a/presence/fpp/fpp_manager_test.cc b/presence/fpp/fpp_manager_test.cc
index b7ed5e72..76dc2fc2 100644
--- a/presence/fpp/fpp_manager_test.cc
+++ b/presence/fpp/fpp_manager_test.cc
@@ -19,6 +19,7 @@
 #include "gmock/gmock.h"
 #include "protobuf-matchers/protocol-buffer-matchers.h"
 #include "gtest/gtest.h"
+#include "presence/implementation/sensor_fusion.h"
 
 namespace nearby {
 namespace presence {
@@ -33,10 +34,12 @@ TEST(FppManager, UpdateBleScanResultSuccess) {
   bool callback_called = false;
   manager.RegisterZoneTransitionListener(
       kCallbackId,
-      [&callback_called](uint64_t device_id,
-                         PresenceZone::DistanceBoundary::RangeType range_type) {
-        callback_called = true;
-      });
+      {.on_proximity_zone_changed =
+           [&callback_called](
+               uint64_t device_id,
+               PresenceZone::DistanceBoundary::RangeType range_type) {
+             callback_called = true;
+           }});
   EXPECT_OK(manager.UpdateBleScanResult(kDeviceId, /*txPower=*/absl::nullopt,
                                         kReachRssi,
                                         /*elapsed_real_time_millis=*/0));
@@ -56,10 +59,12 @@ TEST(FppManager, ZoneTransitionDetected) {
   bool callback_called = false;
   manager.RegisterZoneTransitionListener(
       kCallbackId,
-      [&callback_called](uint64_t device_id,
-                         PresenceZone::DistanceBoundary::RangeType range_type) {
-        callback_called = true;
-      });
+      {.on_proximity_zone_changed =
+           [&callback_called](
+               uint64_t device_id,
+               PresenceZone::DistanceBoundary::RangeType range_type) {
+             callback_called = true;
+           }});
   // ProximityEstimate is only computed after consecutive scans is fulfilled
   EXPECT_OK(manager.UpdateBleScanResult(kDeviceId, /*txPower=*/absl::nullopt,
                                         kReachRssi,
@@ -139,10 +144,12 @@ TEST(FppManager, UpdateBleScanResultWithTxPowerSuccess) {
   bool callback_called = false;
   manager.RegisterZoneTransitionListener(
       kCallbackId,
-      [&callback_called](uint64_t device_id,
-                         PresenceZone::DistanceBoundary::RangeType range_type) {
-        callback_called = true;
-      });
+      {.on_proximity_zone_changed =
+           [&callback_called](
+               uint64_t device_id,
+               PresenceZone::DistanceBoundary::RangeType range_type) {
+             callback_called = true;
+           }});
   EXPECT_OK(manager.UpdateBleScanResult(kDeviceId, /*txPower=*/20, kReachRssi,
                                         /*elapsed_real_time_millis=*/0));
   EXPECT_OK(manager.UpdateBleScanResult(kDeviceId, /*txPower=*/20, kReachRssi,
@@ -159,10 +166,12 @@ TEST(FppManager, UnregisterZoneTransitionListener) {
   bool callback_called = false;
   manager.RegisterZoneTransitionListener(
       kCallbackId,
-      [&callback_called](uint64_t device_id,
-                         PresenceZone::DistanceBoundary::RangeType range_type) {
-        callback_called = true;
-      });
+      {.on_proximity_zone_changed =
+           [&callback_called](
+               uint64_t device_id,
+               PresenceZone::DistanceBoundary::RangeType range_type) {
+             callback_called = true;
+           }});
   EXPECT_OK(manager.UpdateBleScanResult(kDeviceId, /*txPower=*/absl::nullopt,
                                         kReachRssi,
                                         /*elapsed_real_time_millis=*/0));
diff --git a/presence/implementation/BUILD b/presence/implementation/BUILD
index 97fc31b2..a3da0f81 100644
--- a/presence/implementation/BUILD
+++ b/presence/implementation/BUILD
@@ -126,6 +126,7 @@ cc_library(
     ],
     deps = [
         "//presence:types",
+        "@com_google_absl//absl/functional:any_invocable",
         "@com_google_absl//absl/types:optional",
     ],
 )
diff --git a/presence/implementation/sensor_fusion.h b/presence/implementation/sensor_fusion.h
index 452b01fd..027f2225 100644
--- a/presence/implementation/sensor_fusion.h
+++ b/presence/implementation/sensor_fusion.h
@@ -19,6 +19,7 @@
 #include <functional>
 #include <vector>
 
+#include "absl/functional/any_invocable.h"
 #include "absl/types/optional.h"
 #include "presence/device_motion.h"
 #include "presence/presence_zone.h"
@@ -58,16 +59,21 @@ struct RangingData {
   std::vector<DeviceMotion> device_motions;
 };
 
+struct ZoneTransitionCallback {
+  absl::AnyInvocable<void(
+      uint64_t device_id,
+      PresenceZone::DistanceBoundary::RangeType proximity_zone)>
+      on_proximity_zone_changed =
+          [](uint64_t device_id,
+             PresenceZone::DistanceBoundary::RangeType proximity_zone) {};
+  absl::AnyInvocable<void(uint64_t callback_id)> on_callback_id_generated =
+      [](uint64_t callback_id) {};
+};
+
 class SensorFusion {
  public:
   virtual ~SensorFusion() = default;
 
-  // Called when the proximity zone to a nearby peer device has changed.
-  typedef std::function<void(
-      uint64_t device_id,
-      PresenceZone::DistanceBoundary::RangeType proximity_zone)>
-      ZoneTransitionCallback;
-
   // Called when a device motion gesture is detected.
   typedef std::function<void(DeviceMotion::MotionType detected_device_motion)>
       DeviceMotionCallback;