diff --git a/src/device.ts b/src/device.ts
index 4019441..9aa6075 100644
--- a/src/device.ts
+++ b/src/device.ts
@@ -30,7 +30,7 @@ export class SwitchbotDevice {
   _onconnect: () => void;
   _ondisconnect: () => void;
   _ondisconnect_internal: () => void;
-  _onnotify_internal: () => void;
+  _onnotify_internal: (buf: Buffer) => void;
   /* ------------------------------------------------------------------
    * Constructor
    *
@@ -46,6 +46,13 @@ export class SwitchbotDevice {
 
     this._SERV_UUID_PRIMARY = 'cba20d00224d11e69fb80002a5d5c51b';
     this._CHAR_UUID_WRITE = 'cba20002224d11e69fb80002a5d5c51b';
+    this._CHAR_UUID_NOTIFY = 'cba20003224d11e69fb80002a5d5c51b';
+    this._CHAR_UUID_DEVICE = '2a00';
+
+    this._READ_TIMEOUT_MSEC = 3000;
+    this._WRITE_TIMEOUT_MSEC = 3000;
+    this._COMMAND_TIMEOUT_MSEC = 3000;
+
     // Save the device information
     const ad: ad = Advertising.parse(peripheral);
     this._id = ad?.id;
@@ -296,8 +303,8 @@ export class SwitchbotDevice {
           reject(error);
           return;
         }
-        char.on('data', () => { // Remove the argument passed to the _onnotify_internal function
-          this._onnotify_internal();
+        char.on('data', (buf) => { // Remove the argument passed to the _onnotify_internal function
+          this._onnotify_internal(buf);
         });
         resolve();
       });
@@ -459,14 +466,14 @@ export class SwitchbotDevice {
   // Write the specified Buffer data to the write characteristic
   // and receive the response from the notify characteristic
   // with connection handling
-  _command(req_buf) {
+  _command(req_buf: Buffer) {
     return new Promise((resolve, reject) => {
       if (!Buffer.isBuffer(req_buf)) {
         reject(new Error('The specified data is not acceptable for writing.'));
         return;
       }
 
-      let res_buf;
+      let res_buf: Buffer | unknown;
 
       this._connect()
         .then(() => {
@@ -493,15 +500,13 @@ export class SwitchbotDevice {
 
   _waitCommandResponse() {
     return new Promise((resolve, reject) => {
-      const buf: Buffer | null = null;
-
       let timer: NodeJS.Timeout | undefined = setTimeout(() => {
         timer = undefined;
         this._onnotify_internal = () => { };
         reject(new Error('COMMAND_TIMEOUT'));
       }, this._COMMAND_TIMEOUT_MSEC);
 
-      this._onnotify_internal = () => {
+      this._onnotify_internal = (buf) => {
         if (timer) {
           clearTimeout(timer);
           timer = undefined;
diff --git a/src/device/woblindtilt.ts b/src/device/woblindtilt.ts
index b5b30d1..d53ded5 100644
--- a/src/device/woblindtilt.ts
+++ b/src/device/woblindtilt.ts
@@ -4,7 +4,7 @@
  */
 import { Buffer } from 'buffer';
 
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 export class WoBlindTilt extends SwitchbotDevice {
   static parseServiceData(buf, onlog) {
diff --git a/src/device/wobulb.ts b/src/device/wobulb.ts
index 1cc2f7c..38250b3 100644
--- a/src/device/wobulb.ts
+++ b/src/device/wobulb.ts
@@ -4,7 +4,7 @@
  */
 import { Buffer } from 'buffer';
 
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 /**
  * @see https://github.com/OpenWonderLabs/SwitchBotAPI-BLE/blob/latest/devicetypes/colorbulb.md
diff --git a/src/device/wocontact.ts b/src/device/wocontact.ts
index 9cf4713..3232dd4 100644
--- a/src/device/wocontact.ts
+++ b/src/device/wocontact.ts
@@ -2,7 +2,7 @@
  *
  * wocontact.ts: Switchbot BLE API registration.
  */
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 export class WoContact extends SwitchbotDevice {
   static parseServiceData(buf, onlog) {
diff --git a/src/device/wocurtain.ts b/src/device/wocurtain.ts
index 9f966bc..618a8a7 100644
--- a/src/device/wocurtain.ts
+++ b/src/device/wocurtain.ts
@@ -4,7 +4,7 @@
  */
 import { Buffer } from 'buffer';
 
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 export class WoCurtain extends SwitchbotDevice {
   static parseServiceData(buf, onlog) {
diff --git a/src/device/wohand.ts b/src/device/wohand.ts
index d695d9d..5bf16f4 100644
--- a/src/device/wohand.ts
+++ b/src/device/wohand.ts
@@ -1,6 +1,6 @@
 import { Buffer } from 'buffer';
 
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 export class WoHand extends SwitchbotDevice {
   static parseServiceData(buf, onlog) {
diff --git a/src/device/wohumi.ts b/src/device/wohumi.ts
index 308e6be..34c79bf 100644
--- a/src/device/wohumi.ts
+++ b/src/device/wohumi.ts
@@ -1,6 +1,6 @@
 import { Buffer } from 'buffer';
 
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 export class WoHumi extends SwitchbotDevice {
   static parseServiceData(buf, onlog) {
diff --git a/src/device/woiosensorth.ts b/src/device/woiosensorth.ts
index 605f43d..824cd73 100644
--- a/src/device/woiosensorth.ts
+++ b/src/device/woiosensorth.ts
@@ -1,4 +1,4 @@
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 export class WoIOSensorTH extends SwitchbotDevice {
   static parseServiceData(serviceDataBuf, manufacturerDataBuf, onlog) {
diff --git a/src/device/woplugmini.ts b/src/device/woplugmini.ts
index b152467..51dda56 100644
--- a/src/device/woplugmini.ts
+++ b/src/device/woplugmini.ts
@@ -1,6 +1,6 @@
 import { Buffer } from 'buffer';
 
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 /**
  * @see https://github.com/OpenWonderLabs/SwitchBotAPI-BLE/blob/latest/devicetypes/plugmini.md
diff --git a/src/device/wopresence.ts b/src/device/wopresence.ts
index 4facc44..44641e2 100644
--- a/src/device/wopresence.ts
+++ b/src/device/wopresence.ts
@@ -1,4 +1,4 @@
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 export class WoPresence extends SwitchbotDevice {
   static parseServiceData(buf, onlog) {
diff --git a/src/device/wosensorth.ts b/src/device/wosensorth.ts
index 7a22473..81262d8 100644
--- a/src/device/wosensorth.ts
+++ b/src/device/wosensorth.ts
@@ -1,4 +1,4 @@
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 export class WoSensorTH extends SwitchbotDevice {
   static parseServiceData(buf, onlog) {
diff --git a/src/device/wosmartlock.ts b/src/device/wosmartlock.ts
index 61f3121..fab89c6 100644
--- a/src/device/wosmartlock.ts
+++ b/src/device/wosmartlock.ts
@@ -4,7 +4,7 @@
  */
 //import { Buffer } from 'buffer';
 
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 export class WoSmartLock extends SwitchbotDevice {
   static parseServiceData(manufacturerData, onlog) {
diff --git a/src/device/wostrip.ts b/src/device/wostrip.ts
index 5fbb9c1..be8c3cc 100644
--- a/src/device/wostrip.ts
+++ b/src/device/wostrip.ts
@@ -1,6 +1,6 @@
 import { Buffer } from 'buffer';
 
-import { SwitchbotDevice } from '../switchbot.js';
+import { SwitchbotDevice } from '../device.js';
 
 /**
  * @see https://github.com/OpenWonderLabs/SwitchBotAPI-BLE/blob/latest/devicetypes/colorbulb.md
diff --git a/src/switchbot.ts b/src/switchbot.ts
index 3967722..7ebd179 100644
--- a/src/switchbot.ts
+++ b/src/switchbot.ts
@@ -186,7 +186,7 @@ export class SwitchBot {
 
           // Set a handler for the 'discover' event
           this.noble.on('discover', (peripheral) => {
-            const device = SwitchBot.getDeviceObject(peripheral, p.id, p.model) as SwitchbotDevice;
+            const device = this.getDeviceObject(peripheral, p.id, p.model) as SwitchbotDevice;
             if (!device) {
               return;
             }
@@ -265,7 +265,7 @@ export class SwitchBot {
     return promise;
   }
 
-  static getDeviceObject(peripheral, id, model) {
+  getDeviceObject(peripheral, id, model) {
     const ad = Advertising.parse(peripheral, this.onlog);
     if (this.filterAdvertising(ad, id, model)) {
       let device;
@@ -322,7 +322,7 @@ export class SwitchBot {
     }
   }
 
-  static filterAdvertising(ad, id, model) {
+  filterAdvertising(ad, id, model) {
     if (!ad) {
       return false;
     }
@@ -451,7 +451,7 @@ export class SwitchBot {
           // Set a handler for the 'discover' event
           this.noble.on('discover', (peripheral) => {
             const ad = Advertising.parse(peripheral, this.onlog);
-            if (SwitchBot.filterAdvertising(ad, p.id, p.model)) {
+            if (this.filterAdvertising(ad, p.id, p.model)) {
               if (
                 this.onadvertisement &&
                 typeof this.onadvertisement === 'function'