diff --git a/device/vr/vr_device_manager.cc b/device/vr/vr_device_manager.cc
index a67153c..0b16cf6 100644
--- a/device/vr/vr_device_manager.cc
+++ b/device/vr/vr_device_manager.cc
@@ -75,6 +75,26 @@
   return g_vr_device_manager;
 }
 
+// Returns the requested device with the requested id if the specified service
+// is allowed to access it.
+VRDevice* VRDeviceManager::GetAllowedDevice(
+    VRServiceImpl* service, unsigned int index) {
+  VRDeviceManager* device_manager = GetInstance();
+
+  // If another service is presenting to the requested device don't allow other
+  // services to access it. That could potentially allow them to spy on
+  // where the user is looking on another page, spam another application with
+  // pose resets, etc.
+  if (device_manager->presenting_service_ &&
+      device_manager->presenting_service_ != service) {
+    if (device_manager->presenting_device_ &&
+        device_manager->presenting_device_->id() == index)
+      return nullptr;
+  }
+
+  return device_manager->GetDevice(index);
+}
+
 void VRDeviceManager::SetInstance(VRDeviceManager* instance) {
   // Unit tests can create multiple instances but only one should exist at any
   // given time so g_vr_device_manager should only go from nullptr to
@@ -101,6 +121,13 @@
   services_.erase(std::remove(services_.begin(), services_.end(), service),
                   services_.end());
 
+  if (service == presenting_service_) {
+    presenting_device_->ExitPresent();
+
+    presenting_service_ = nullptr;
+    presenting_device_ = nullptr;
+  }
+
   if (services_.empty() && !keep_alive_) {
     // Delete the device manager when it has no active connections.
     // delete g_vr_device_manager;
@@ -205,7 +232,7 @@
 
   // Tell the device to stop presenting.
   presenting_device_->ExitPresent();
-  presenting_service_->client()->OnExitPresent(presenting_device_->id());
+  presenting_service_->client()->OnExitPresent(index);
 
   // Clear the presenting service and device.
   presenting_service_ = nullptr;
diff --git a/device/vr/vr_device_manager.h b/device/vr/vr_device_manager.h
index f269fdb..cc3b5b0a 100644
--- a/device/vr/vr_device_manager.h
+++ b/device/vr/vr_device_manager.h
@@ -32,13 +32,15 @@
   // Returns the VRDeviceManager singleton.
   static VRDeviceManager* GetInstance();
 
+  // Gets a VRDevice instance if the specified service is allowed to access it.
+  static VRDevice* GetAllowedDevice(VRServiceImpl* service, unsigned int index);
+
   // Adds a listener for device manager events. VRDeviceManager does not own
   // this object.
   void AddService(VRServiceImpl* service);
   void RemoveService(VRServiceImpl* service);
 
   DEVICE_VR_EXPORT mojo::Array<VRDisplayPtr> GetVRDevices();
-  DEVICE_VR_EXPORT VRDevice* GetDevice(unsigned int index);
 
   // Manage presentation to only allow a single service and device at a time.
   bool RequestPresent(VRServiceImpl* service, unsigned int index);
@@ -65,6 +67,8 @@
   DEVICE_VR_EXPORT explicit VRDeviceManager(
       std::unique_ptr<VRDeviceProvider> provider);
 
+  VRDevice* GetDevice(unsigned int index);
+
   static void SetInstance(VRDeviceManager* service);
   static bool HasInstance();
 
diff --git a/device/vr/vr_service.mojom b/device/vr/vr_service.mojom
index 945d59c..1ef3d9e 100644
--- a/device/vr/vr_service.mojom
+++ b/device/vr/vr_service.mojom
@@ -74,7 +74,7 @@
 
   GetDisplays() => (array<VRDisplay> displays);
   [Sync]
-  GetPose(uint32 index) => (VRPose pose);
+  GetPose(uint32 index) => (VRPose? pose);
   ResetPose(uint32 index);
 
   RequestPresent(uint32 index) => (bool success);
diff --git a/device/vr/vr_service_impl.cc b/device/vr/vr_service_impl.cc
index 3b70aeb..6881a60 100644
--- a/device/vr/vr_service_impl.cc
+++ b/device/vr/vr_service_impl.cc
@@ -48,8 +48,7 @@
 }
 
 void VRServiceImpl::GetPose(uint32_t index, const GetPoseCallback& callback) {
-  VRDeviceManager* device_manager = VRDeviceManager::GetInstance();
-  VRDevice* device = device_manager->GetDevice(index);
+  VRDevice* device = VRDeviceManager::GetAllowedDevice(this, index);
 
   if (device) {
     callback.Run(device->GetPose());
@@ -59,8 +58,7 @@
 }
 
 void VRServiceImpl::ResetPose(uint32_t index) {
-  VRDeviceManager* device_manager = VRDeviceManager::GetInstance();
-  VRDevice* device = device_manager->GetDevice(index);
+  VRDevice* device = VRDeviceManager::GetAllowedDevice(this, index);
   if (device)
     device->ResetPose();
 }
@@ -84,8 +82,7 @@
 void VRServiceImpl::UpdateLayerBounds(uint32_t index,
                                       VRLayerBoundsPtr leftBounds,
                                       VRLayerBoundsPtr rightBounds) {
-  VRDeviceManager* device_manager = VRDeviceManager::GetInstance();
-  VRDevice* device = device_manager->GetDevice(index);
+  VRDevice* device = VRDeviceManager::GetAllowedDevice(this, index);
   if (device)
     device->UpdateLayerBounds(std::move(leftBounds), std::move(rightBounds));
 }