diff --git a/ui/pi-web-agent-app/src/app/pi-control.service.ts b/ui/pi-web-agent-app/src/app/pi-control.service.ts
index 26afc054..fe4ef15b 100644
--- a/ui/pi-web-agent-app/src/app/pi-control.service.ts
+++ b/ui/pi-web-agent-app/src/app/pi-control.service.ts
@@ -14,21 +14,21 @@ export class PiControlService {
   currentMessage: Observable<any> = this.messageSource.asObservable();
 
   constructor(
-    private _zone: NgZone,
+    private zone: NgZone,
     private websocketService: WebsocketService
   ) {
     this.websocketService.connect((next: any) => this.messageSource.next(next));
   }
 
-  commandSink() {
+  commandSink(): Subject<any> | null {
     return this.websocketService.subject;
   }
 
-  eventSource() {
+  eventSource(): Observable<any> {
     return this.currentMessage;
   }
 
-  sendCommand(command: PiCommand) {
+  sendCommand(command: PiCommand): void {
     this.commandSink()?.next(command);
   }
 
@@ -38,13 +38,13 @@ export class PiControlService {
       const observable = new Observable(
         (observer: Observer<any>) => {
           observer.next = event => {
-            this._zone.run(() => {
+            this.zone.run(() => {
               this.sendCommand(event);
             });
           };
 
           observer.error = error => {
-            this._zone.run( () => {
+            this.zone.run( () => {
               observer.error(error);
             });
           };
diff --git a/ui/pi-web-agent-app/src/app/system-info.service.ts b/ui/pi-web-agent-app/src/app/system-info.service.ts
index df3952ce..90f978c9 100644
--- a/ui/pi-web-agent-app/src/app/system-info.service.ts
+++ b/ui/pi-web-agent-app/src/app/system-info.service.ts
@@ -12,7 +12,7 @@ export class SystemInfoService {
   }
 
 
-  fetchSystemInfo() {
+  fetchSystemInfo(): void {
     this.piControlService.sendCommand({Action_Type: 'DISPLAY_LIVE_INFO'});
   }
 }
diff --git a/ui/pi-web-agent-app/src/app/websocket.service.ts b/ui/pi-web-agent-app/src/app/websocket.service.ts
index f294ac90..d1938ae3 100644
--- a/ui/pi-web-agent-app/src/app/websocket.service.ts
+++ b/ui/pi-web-agent-app/src/app/websocket.service.ts
@@ -11,12 +11,12 @@ export class WebsocketService {
   constructor() {
   }
 
-  private url() {
+  private url(): string {
     const protocol = window.location.protocol.replace('http', 'ws');
     const host = window.location.host;
     return `${protocol}//${host}/api/control/stream`;
   }
-  public connect(subscriber: (next: any) => void)  {
+  public connect(subscriber: (next: any) => void): void  {
     try {
       if (!this.subject) {
         console.log(`Connecting to ${this.url()} for the first time`);
@@ -29,7 +29,7 @@ export class WebsocketService {
     }
   }
 
-  sendMessage(event: any) {
+  sendMessage(event: any): void {
     this.subject?.next(event);
   }