diff --git a/src/lib/services/generic.service.ts b/src/lib/services/generic.service.ts
index b879393..5d12fb0 100644
--- a/src/lib/services/generic.service.ts
+++ b/src/lib/services/generic.service.ts
@@ -1,8 +1,8 @@
 import { HttpClient, HttpEvent, HttpParams } from '@angular/common/http';
 import { Injector } from '@angular/core';
 import { Observable } from 'rxjs';
-import { CustomHttpUrlEncodingCodec, List, RequiredParam, Validate } from '../utils';
-import { HeadersConfiguration } from '../utils/headers-configuration';
+import { CustomHttpUrlEncodingCodec, HeadersConfiguration, List, RequiredParam, Validate } from '../utils';
+import { map, tap } from 'rxjs/operators';
 
 export interface HeaderOptions {
     readonly authorization?: boolean;
@@ -21,23 +21,35 @@ export interface QueryParam {
  */
 export abstract class GenericService<I> {
     protected readonly _http = this._injector.get(HttpClient);
+    private _lastCheckedForChanges = '0';
 
     protected constructor(protected readonly _injector: Injector, protected readonly _defaultModelPath: string) {}
 
+    protected get _hasChanges$(): Observable<boolean> {
+        return this._post<{ value: boolean }>({ since: this._lastCheckedForChanges }, `${this._defaultModelPath}/changes`).pipe(
+            map(res => res.value),
+            tap(() => this._updateLastChanged()),
+        );
+    }
+
     get<T = I[]>(): Observable<T>;
+
     // eslint-disable-next-line @typescript-eslint/unified-signatures
     get<T = I>(id: string, ...args: unknown[]): Observable<T>;
+
     // eslint-disable-next-line @typescript-eslint/no-unused-vars
     get<T>(id?: string, ...args: unknown[]): Observable<T> {
         return id ? this._getOne<T>([id]) : this.getAll<T>();
     }
 
     getAll<R = I[]>(modelPath = this._defaultModelPath, queryParams?: List<QueryParam>): Observable<R> {
-        return this._http.get<R>(`/${encodeURI(modelPath)}`, {
-            headers: HeadersConfiguration.getHeaders({ contentType: false }),
-            observe: 'body',
-            params: this._queryParams(queryParams),
-        });
+        return this._http
+            .get<R>(`/${encodeURI(modelPath)}`, {
+                headers: HeadersConfiguration.getHeaders({ contentType: false }),
+                observe: 'body',
+                params: this._queryParams(queryParams),
+            })
+            .pipe(tap(() => this._updateLastChanged()));
     }
 
     @Validate()
@@ -64,8 +76,7 @@ export abstract class GenericService<I> {
             formParams.append('file', data);
         }
 
-        // TODO: Fix getHeaders()?
-        const headers = HeadersConfiguration.getHeaders().delete('content-type');
+        const headers = HeadersConfiguration.getHeaders({ contentType: false });
 
         return this._http.post<R>(`/${encodeURI(modelPath)}`, formParams, {
             headers,
@@ -125,4 +136,8 @@ export abstract class GenericService<I> {
 
         return queryParameters;
     }
+
+    protected _updateLastChanged(): void {
+        this._lastCheckedForChanges = new Date().toISOString();
+    }
 }