diff --git a/Sources/App/API/Message.swift b/Sources/App/API/Message.swift
index b29024c..90d2b2d 100644
--- a/Sources/App/API/Message.swift
+++ b/Sources/App/API/Message.swift
@@ -29,6 +29,14 @@ struct Message: Equatable, Hashable {
     }
 }
 
+extension Message: Codable {
+
+    enum CodingKeys: Int, CodingKey {
+        case mac = 1
+        case content = 2
+    }
+}
+
 extension Message {
 
     /**
@@ -42,14 +50,17 @@ extension Message {
         /// The counter of the message (for freshness)
         let id: UInt32
 
+        let deviceId: UInt8?
+
         /**
          Create new message content.
          - Parameter time: The time of message creation,
          - Parameter id: The counter of the message
          */
-        init(time: UInt32, id: UInt32) {
+        init(time: UInt32, id: UInt32, device: UInt8) {
             self.time = time
             self.id = id
+            self.deviceId = device
         }
 
         /**
@@ -61,20 +72,29 @@ extension Message {
          */
         init<T: Sequence>(decodeFrom data: T) where T.Element == UInt8 {
             self.time = UInt32(data: Data(data.prefix(MemoryLayout<UInt32>.size)))
-            self.id = UInt32(data: Data(data.dropFirst(MemoryLayout<UInt32>.size)))
+            self.id = UInt32(data: Data(data.dropLast().suffix(MemoryLayout<UInt32>.size)))
+            self.deviceId = data.suffix(1).last!
         }
 
         /// The byte length of an encoded message content
         static var length: Int {
-            MemoryLayout<UInt32>.size * 2
+            MemoryLayout<UInt32>.size * 2 + 1
         }
 
         /// The message content encoded to data
         var encoded: Data {
-            time.encoded + id.encoded
+            time.encoded + id.encoded + Data([deviceId ?? 0])
         }
     }
+}
 
+extension Message.Content: Codable {
+
+    enum CodingKeys: Int, CodingKey {
+        case time = 1
+        case id = 2
+        case deviceId = 3
+    }
 }
 
 extension Message {
@@ -96,6 +116,14 @@ extension Message {
         self.init(decodeFrom: data)
     }
 
+    init?(decodeFrom data: Data, index: inout Int) {
+        guard index + Message.length <= data.count else {
+            return nil
+        }
+        self.init(decodeFrom: data.advanced(by: index))
+        index += Message.length
+    }
+
     /// The message encoded to data
     var encoded: Data {
         mac + content.encoded
diff --git a/Sources/App/API/MessageResult.swift b/Sources/App/API/MessageResult.swift
index ecf41af..ccfbf71 100644
--- a/Sources/App/API/MessageResult.swift
+++ b/Sources/App/API/MessageResult.swift
@@ -26,6 +26,9 @@ enum MessageResult: UInt8 {
     /// The key was accepted by the device, and the door will be opened
     case messageAccepted = 7
 
+    /// The device id is invalid
+    case messageDeviceInvalid = 8
+
 
     /// The request did not contain body data with the key
     case noBodyData = 10
@@ -61,6 +64,8 @@ extension MessageResult: CustomStringConvertible {
             return "Message counter invalid"
         case .messageAccepted:
             return "Message accepted"
+        case .messageDeviceInvalid:
+            return "Invalid device ID"
         case .noBodyData:
             return "No body data included in the request"
         case .deviceNotConnected:
diff --git a/Tests/AppTests/AppTests.swift b/Tests/AppTests/AppTests.swift
index 7ec1983..7d12bd8 100644
--- a/Tests/AppTests/AppTests.swift
+++ b/Tests/AppTests/AppTests.swift
@@ -11,7 +11,7 @@ final class AppTests: XCTestCase {
     }
 
     func testEncodingContent() {
-        let input = Message.Content(time: 1234567890, id: 23456789)
+        let input = Message.Content(time: 1234567890, id: 23456789, device: 0)
         let data = Array(input.encoded)
         let output = Message.Content(decodeFrom: data)
         XCTAssertEqual(input, output)
@@ -22,7 +22,7 @@ final class AppTests: XCTestCase {
 
     func testEncodingMessage() {
         let input = Message(mac: Data(repeating: 42, count: 32),
-                            content: Message.Content(time: 1234567890, id: 23456789))
+                            content: Message.Content(time: 1234567890, id: 23456789, device: 0))
         let data = input.encoded
         let buffer = ByteBuffer(data: data)
         let output = Message(decodeFrom: buffer)
@@ -31,7 +31,7 @@ final class AppTests: XCTestCase {
 
     func testSigning() throws {
         let key = SymmetricKey(size: .bits256)
-        let content = Message.Content(time: 1234567890, id: 23456789)
+        let content = Message.Content(time: 1234567890, id: 23456789, device: 0)
         let input = content.authenticate(using: key)
         XCTAssertTrue(input.isValid(using: key))