diff --git a/examples/debug_d3/src/debug.c b/examples/debug_d3/src/debug.c
index 2e0121c..3308af7 100644
--- a/examples/debug_d3/src/debug.c
+++ b/examples/debug_d3/src/debug.c
@@ -47,20 +47,13 @@ void test3(uint64_t timestamp,
 }
 
 int main(int argc, const char** argv) {
-	device3_type* dev3 = device3_open(test3);
-	
-	if (!dev3) {
+	device3_type dev3;
+	if (DEVICE3_ERROR_NO_ERROR != device3_open(&dev3, test3)) {
 		return 1;
 	}
 	
-	device3_clear(dev3);
-	
-	while (dev3) {
-		if (device3_read(dev3, -1) != DEVICE3_ERROR_NO_ERROR) {
-			break;
-		}
-	}
-	
-	device3_close(dev3);
+	device3_clear(&dev3);
+	while (DEVICE3_ERROR_NO_ERROR == device3_read(&dev3, -1));
+	device3_close(&dev3);
 	return 0;
 }
diff --git a/examples/debug_d4/src/debug.c b/examples/debug_d4/src/debug.c
index 82a27b8..df0b4af 100644
--- a/examples/debug_d4/src/debug.c
+++ b/examples/debug_d4/src/debug.c
@@ -46,20 +46,13 @@ void test4(uint64_t timestamp,
 }
 
 int main(int argc, const char** argv) {
-	device4_type* dev4 = device4_open(test4);
-	
-	if (!dev4) {
+	device4_type dev4;
+	if (DEVICE4_ERROR_NO_ERROR != device4_open(&dev4, test4)) {
 		return 1;
 	}
 	
-	device4_clear(dev4);
-	
-	while (dev4) {
-		if (device4_read(dev4, 1000) != DEVICE4_ERROR_NO_ERROR) {
-			break;
-		}
-	}
-	
-	device4_close(dev4);
+	device4_clear(&dev4);
+	while (DEVICE4_ERROR_NO_ERROR == device4_read(&dev4, -1));
+	device4_close(&dev4);
 	return 0;
 }
diff --git a/examples/mcu_firmware/src/upgrade.c b/examples/mcu_firmware/src/upgrade.c
index 5c95dc7..3b2ccc8 100644
--- a/examples/mcu_firmware/src/upgrade.c
+++ b/examples/mcu_firmware/src/upgrade.c
@@ -67,14 +67,13 @@ int main(int argc, const char** argv) {
         return 0;
     }
 
-	device4_type* dev4 = device4_open(NULL);
-	
-	if (!dev4) {
+	device4_type dev4;
+	if (DEVICE4_ERROR_NO_ERROR != device4_open(&dev4, NULL)) {
 		return 1;
 	}
 	
-	device4_clear(dev4);
-	device4_update_mcu_firmware(dev4, path);
-	device4_close(dev4);
+	device4_clear(&dev4);
+	device4_update_mcu_firmware(&dev4, path);
+	device4_close(&dev4);
 	return 0;
 }
diff --git a/interface_lib/include/device3.h b/interface_lib/include/device3.h
index f146322..e660783 100644
--- a/interface_lib/include/device3.h
+++ b/interface_lib/include/device3.h
@@ -60,7 +60,9 @@ enum device3_error_t {
 	DEVICE3_ERROR_UNEXPECTED = 10,
 	DEVICE3_ERROR_WRONG_SIGNATURE = 11,
 	DEVICE3_ERROR_INVALID_VALUE = 12,
-	DEVICE3_ERROR_UNKNOWN = 13,
+	DEVICE3_ERROR_NOT_INITIALIZED = 13,
+	DEVICE3_ERROR_PAYLOAD_FAILED = 14,
+	DEVICE3_ERROR_UNKNOWN = 15,
 };
 
 struct __attribute__((__packed__)) device3_packet_t {
@@ -144,7 +146,7 @@ struct device3_t {
 
 typedef struct device3_t device3_type;
 
-device3_type* device3_open(device3_event_callback callback);
+device3_error_type device3_open(device3_type* device, device3_event_callback callback);
 
 device3_error_type device3_reset_calibration(device3_type* device);
 
diff --git a/interface_lib/include/device4.h b/interface_lib/include/device4.h
index f2e6a2f..fd5482e 100644
--- a/interface_lib/include/device4.h
+++ b/interface_lib/include/device4.h
@@ -107,7 +107,9 @@ enum device4_error_t {
 	DEVICE4_ERROR_UNEXPECTED = 6,
 	DEVICE4_ERROR_WRONG_HEAD = 7,
 	DEVICE4_ERROR_INVALID_LENGTH = 8,
-	DEVICE4_ERROR_UNKNOWN = 9,
+	DEVICE4_ERROR_NOT_INITIALIZED = 9,
+	DEVICE4_ERROR_PAYLOAD_FAILED = 10,
+	DEVICE4_ERROR_UNKNOWN = 11,
 };
 
 struct __attribute__((__packed__)) device4_packet_t {
@@ -162,7 +164,7 @@ struct device4_t {
 
 typedef struct device4_t device4_type;
 
-device4_type* device4_open(device4_event_callback callback);
+device4_error_type device4_open(device4_type* device, device4_event_callback callback);
 
 device4_error_type device4_clear(device4_type* device);
 
diff --git a/interface_lib/src/device3.c b/interface_lib/src/device3.c
index a393035..6f6c709 100644
--- a/interface_lib/src/device3.c
+++ b/interface_lib/src/device3.c
@@ -181,12 +181,10 @@ static FusionQuaternion json_object_get_quaternion(struct json_object* obj) {
 	return quaternion;
 }
 
-device3_type* device3_open(device3_event_callback callback) {
-	device3_type* device = (device3_type*) malloc(sizeof(device3_type));
-	
+device3_error_type device3_open(device3_type* device, device3_event_callback callback) {
 	if (!device) {
-		device3_error("Not allocated");
-		return NULL;
+		device3_error("No device");
+		return DEVICE3_ERROR_NO_DEVICE;
 	}
 	
 	memset(device, 0, sizeof(device3_type));
@@ -196,7 +194,7 @@ device3_type* device3_open(device3_event_callback callback) {
 	
 	if (0 != hid_init()) {
 		device3_error("Not initialized");
-		return device;
+		return DEVICE3_ERROR_NOT_INITIALIZED;
 	}
 
 	struct hid_device_info* info = hid_enumerate(
@@ -218,14 +216,14 @@ device3_type* device3_open(device3_event_callback callback) {
 	
 	if (!device->handle) {
 		device3_error("No handle");
-		return device;
+		return DEVICE3_ERROR_NO_HANDLE;
 	}
 
 	device3_clear(device);
 	
 	if (!send_payload_msg(device, DEVICE3_MSG_GET_STATIC_ID, 0, NULL)) {
 		device3_error("Failed sending payload to get static id");
-		return device;
+		return DEVICE3_ERROR_PAYLOAD_FAILED;
 	}
 	
 	uint32_t static_id = 0;
@@ -240,7 +238,7 @@ device3_type* device3_open(device3_event_callback callback) {
 	
 	if (!send_payload_msg(device, DEVICE3_MSG_GET_CAL_DATA_LENGTH, 0, NULL)) {
 		device3_error("Failed sending payload to get calibration data length");
-		return device;
+		return DEVICE3_ERROR_PAYLOAD_FAILED;
 	}
 	
 	uint32_t calibration_len = 0;
@@ -296,7 +294,7 @@ device3_type* device3_open(device3_event_callback callback) {
 	
 	if (!send_payload_msg_signal(device, DEVICE3_MSG_START_IMU_DATA, 0x1)) {
 		device3_error("Failed sending payload to start imu data stream");
-		return device;
+		return DEVICE3_ERROR_PAYLOAD_FAILED;
 	}
 	
 	const uint32_t SAMPLE_RATE = 1000;
@@ -316,7 +314,7 @@ device3_type* device3_open(device3_event_callback callback) {
 	};
 	
 	FusionAhrsSetSettings((FusionAhrs*) device->ahrs, &settings);
-	return device;
+	return DEVICE3_ERROR_NO_ERROR;
 }
 
 device3_error_type device3_reset_calibration(device3_type* device) {
@@ -896,10 +894,9 @@ device3_error_type device3_close(device3_type* device) {
 
 	if (device->handle) {
 		hid_close(device->handle);
-		device->handle = NULL;
 	}
 	
-	free(device);
+	memset(device, 0, sizeof(device3_type));
 	hid_exit();
 
 	return DEVICE3_ERROR_NO_ERROR;
diff --git a/interface_lib/src/device4.c b/interface_lib/src/device4.c
index 7e5da18..aa57d56 100644
--- a/interface_lib/src/device4.c
+++ b/interface_lib/src/device4.c
@@ -165,12 +165,10 @@ static bool do_payload_action(device4_type* device, uint16_t msgid, uint8_t len,
 	return false;
 }
 
-device4_type* device4_open(device4_event_callback callback) {
-	device4_type* device = (device4_type*) malloc(sizeof(device4_type));
-	
+device4_error_type device4_open(device4_type* device, device4_event_callback callback) {
 	if (!device) {
-		device4_error("Not allocated");
-		return NULL;
+		device4_error("No device");
+		return DEVICE4_ERROR_NO_DEVICE;
 	}
 	
 	memset(device, 0, sizeof(device4_type));
@@ -180,7 +178,7 @@ device4_type* device4_open(device4_event_callback callback) {
 
 	if (0 != hid_init()) {
 		device4_error("Not initialized");
-		return device;
+		return DEVICE4_ERROR_NOT_INITIALIZED;
 	}
 
 	struct hid_device_info* info = hid_enumerate(
@@ -202,57 +200,57 @@ device4_type* device4_open(device4_event_callback callback) {
 
 	if (!device->handle) {
 		device4_error("No handle");
-		return device;
+		return DEVICE4_ERROR_NO_HANDLE;
 	}
 
 	device4_clear(device);
 
 	if (!send_payload_action(device, DEVICE4_MSG_R_ACTIVATION_TIME, 0, NULL)) {
 		device4_error("Requesting activation time failed");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	uint8_t activated;
 	if (!recv_payload_msg(device, DEVICE4_MSG_R_ACTIVATION_TIME, 1, &activated)) {
 		device4_error("Receiving activation time failed");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	device->activated = (activated != 0);
 
 	if (!device->activated) {
 		device4_error("Device is not activated");
-		return device;
+		return DEVICE4_ERROR_NO_ACTIVATION;
 	}
 
 	if (!send_payload_action(device, DEVICE4_MSG_R_MCU_APP_FW_VERSION, 0, NULL)) {
 		device4_error("Requesting current MCU app firmware version");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	if (!recv_payload_msg(device, DEVICE4_MSG_R_MCU_APP_FW_VERSION, 41, (uint8_t*) device->mcu_app_fw_version)) {
 		device4_error("Receiving current MCU app firmware version failed");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	if (!send_payload_action(device, DEVICE4_MSG_R_DP7911_FW_VERSION, 0, NULL)) {
 		device4_error("Requesting current DP firmware version");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	if (!recv_payload_msg(device, DEVICE4_MSG_R_DP7911_FW_VERSION, 41, (uint8_t*) device->dp_fw_version)) {
 		device4_error("Receiving current DP firmware version failed");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	if (!send_payload_action(device, DEVICE4_MSG_R_DSP_APP_FW_VERSION, 0, NULL)) {
 		device4_error("Requesting current DSP app firmware version");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	if (!recv_payload_msg(device, DEVICE4_MSG_R_DSP_APP_FW_VERSION, 41, (uint8_t*) device->dsp_fw_version)) {
 		device4_error("Receiving current DSP app firmware version failed");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 #ifndef NDEBUG
@@ -263,22 +261,22 @@ device4_type* device4_open(device4_event_callback callback) {
 
 	if (!send_payload_action(device, DEVICE4_MSG_R_BRIGHTNESS, 0, NULL)) {
 		device4_error("Requesting initial brightness failed");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	if (!recv_payload_msg(device, DEVICE4_MSG_R_BRIGHTNESS, 1, &device->brightness)) {
 		device4_error("Receiving initial brightness failed");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	if (!send_payload_action(device, DEVICE4_MSG_R_DISP_MODE, 0, NULL)) {
 		device4_error("Requesting display mode failed");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 	if (!recv_payload_msg(device, DEVICE4_MSG_R_DISP_MODE, 1, &device->disp_mode)) {
 		device4_error("Receiving display mode failed");
-		return device;
+		return DEVICE4_ERROR_PAYLOAD_FAILED;
 	}
 
 #ifndef NDEBUG
@@ -286,7 +284,7 @@ device4_type* device4_open(device4_event_callback callback) {
 	printf("Disp-Mode: %d\n", device->disp_mode);
 #endif
 
-	return device;
+	return DEVICE4_ERROR_NO_ERROR;
 }
 
 static void device4_callback(device4_type* device,
@@ -576,10 +574,9 @@ device4_error_type device4_close(device4_type* device) {
 	
 	if (device->handle) {
 		hid_close(device->handle);
-		device->handle = NULL;
 	}
 	
-	free(device);
+	memset(device, 0, sizeof(device4_type));
 	hid_exit();
 
 	return DEVICE4_ERROR_NO_ERROR;
diff --git a/src/driver.c b/src/driver.c
index 9a82730..a50e131 100644
--- a/src/driver.c
+++ b/src/driver.c
@@ -102,30 +102,29 @@ int main(int argc, const char** argv) {
 	}
 	
 	if (pid == 0) {
-		device3_type* dev3 = device3_open(test3);
-		device3_clear(dev3);
-		
-		while (dev3) {
-			if (device3_read(dev3, 0) != DEVICE3_ERROR_NO_ERROR) {
-				break;
-			}
+		device3_type dev3;
+		if (DEVICE3_ERROR_NO_ERROR != device3_open(&dev3, test3)) {
+			return 1;
 		}
-		
-		device3_close(dev3);
+
+		device3_clear(&dev3);
+		while (DEVICE3_ERROR_NO_ERROR == device3_read(&dev3, 0));
+		device3_close(&dev3);
 		return 0;
 	} else {
-		device4_type* dev4 = device4_open(test4);
-		device4_clear(dev4);
-		
-		while (dev4) {
-			if (device4_read(dev4, 0) != DEVICE4_ERROR_NO_ERROR) {
-				break;
-			}
-		}
-		
-		device4_close(dev4);
-		
 		int status = 0;
+
+		device4_type dev4;
+		if (DEVICE4_ERROR_NO_ERROR != device4_open(&dev4, test4)) {
+			status = 1;
+			goto exit;
+		}
+
+		device4_clear(&dev4);
+		while (DEVICE4_ERROR_NO_ERROR == device4_read(&dev4, 0));
+		device4_close(&dev4);
+		
+	exit:
 		if (pid != waitpid(pid, &status, 0)) {
 			return 1;
 		}