diff --git a/src/colordistancesensor.ts b/src/colordistancesensor.ts
index 306b892..5506677 100644
--- a/src/colordistancesensor.ts
+++ b/src/colordistancesensor.ts
@@ -9,15 +9,16 @@ export class ColorDistanceSensor extends Device {
         super(hub, portId, Consts.DeviceType.COLOR_DISTANCE_SENSOR);
 
         this.on("newListener", (event) => {
-            switch (event) {
-                case "color":
-                    this.subscribe(0x00);
-                    break;
-                case "distance":
-                    this.subscribe(0x01);
-                    break;
+            if (this.autoSubscribe) {
+                switch (event) {
+                    case "color":
+                        this.subscribe(0x00);
+                        break;
+                    case "distance":
+                        this.subscribe(0x01);
+                        break;
+                }
             }
-
         });
 
     }
diff --git a/src/device.ts b/src/device.ts
index 8fe202e..4ed700e 100644
--- a/src/device.ts
+++ b/src/device.ts
@@ -5,6 +5,8 @@ import * as Consts from "./consts";
 
 export class Device extends EventEmitter {
 
+    public autoSubscribe: boolean = true;
+
     private _hub: Hub;
     private _portId: number;
     private _connected: boolean = true;
@@ -18,7 +20,7 @@ export class Device extends EventEmitter {
         this._portId = portId;
         this._type = type;
         this.hub.on("detach", (device) => {
-            if (device.portId === this.portId) {
+            if (device === this) {
                 this._connected = false;
                 this.emit("detach");
             }
@@ -46,6 +48,9 @@ export class Device extends EventEmitter {
     }
 
     public send (data: Buffer, characteristic: string = Consts.BLECharacteristic.LPF2_ALL, callback?: () => void) {
+        if (!this.connected) {
+            throw new Error("Device is not connected");
+        }
         this.hub.send(data, characteristic, callback);
     }
 
diff --git a/src/hub.ts b/src/hub.ts
index 323f53d..36fe735 100644
--- a/src/hub.ts
+++ b/src/hub.ts
@@ -21,7 +21,7 @@ export class Hub extends EventEmitter {
     public useSpeedMap: boolean = true;
     protected _type: Consts.HubType = Consts.HubType.UNKNOWN;
 
-    protected _attachedDevices: Device[] = [];
+    protected _attachedDevices: {[portId: number]: Device} = {};
 
     protected _portNames: {[port: string]: number} = {};
     // protected _virtualPorts: {[port: string]: Port} = {};
@@ -176,7 +176,6 @@ export class Hub extends EventEmitter {
 
     public getPortNameForPortId (portId: number) {
         for (const port of Object.keys(this._portNames)) {
-            console.log(port);
             if (this._portNames[port] === portId) {
                 return port;
             }
@@ -285,13 +284,7 @@ export class Hub extends EventEmitter {
 
     protected _attachDevice (device: Device) {
 
-        const exists = this._getDeviceByPortId(device.portId);
-
-        if (exists) {
-            this._attachedDevices.splice(this._attachedDevices.findIndex((attachedDevice) => attachedDevice.portId === device.portId), 1);
-        } else {
-            this._attachedDevices.push(device);
-        }
+        this._attachedDevices[device.portId] = device;
 
         /**
          * Emits when a device is attached to the Hub.
@@ -330,7 +323,7 @@ export class Hub extends EventEmitter {
 
 
     protected _detachDevice (device: Device) {
-        this._attachedDevices.splice(this._attachedDevices.findIndex((attachedDevice) => attachedDevice.portId === device.portId), 1);
+        delete this._attachedDevices[device.portId];
         /**
          * Emits when a device is detached from the Hub.
          * @event Hub#attach
@@ -341,7 +334,7 @@ export class Hub extends EventEmitter {
 
 
     protected _getDeviceByPortId (portId: number) {
-        return this._attachedDevices.find((attachedDevice) => attachedDevice.portId === portId);
+        return this._attachedDevices[portId];
     }