diff --git a/src/app/components/contacts/contact-detail/contact-detail.component.html b/src/app/components/contacts/contact-detail/contact-detail.component.html
index 5a8c6d9..b0b01fd 100644
--- a/src/app/components/contacts/contact-detail/contact-detail.component.html
+++ b/src/app/components/contacts/contact-detail/contact-detail.component.html
@@ -89,7 +89,9 @@
         @if(selectedUser.isOnline) {
         <span>{{ "contacts.contactLastOnlineTxt" | translate }}</span>
         } @else {
-        <span>{{ convertTimestamp(selectedUser.lastLogin) }}</span>
+        <span
+          >{{ selectedUser.lastLogin | date : "dd. MMM yyyy, HH:mm:ss" }}
+        </span>
         } }
       </div>
     </div>
diff --git a/src/app/components/contacts/contact-detail/contact-detail.component.ts b/src/app/components/contacts/contact-detail/contact-detail.component.ts
index ece327e..8cc59e9 100644
--- a/src/app/components/contacts/contact-detail/contact-detail.component.ts
+++ b/src/app/components/contacts/contact-detail/contact-detail.component.ts
@@ -25,7 +25,7 @@ import { User } from '../../../interfaces/user.interface';
   styleUrl: './contact-detail.component.scss',
 })
 export class ContactDetailComponent {
-  @Input() selectedUserId: string | undefined;
+  @Input() selectedUserId: string | null = null;
   @Input() currentUser: User | null = null;
   @Output() closeContactEmitter = new EventEmitter<boolean>();
 
@@ -33,11 +33,9 @@ export class ContactDetailComponent {
   selectedUser: User | null = null;
 
   constructor(
-    private router: Router,
     public sharedService: SharedService,
     public firebaseService: FirebaseService,
-    private userService: UserService,
-    private languageService: LanguageService
+    private userService: UserService
   ) {}
 
   ngOnChanges(changes: SimpleChanges) {
@@ -110,89 +108,6 @@ export class ContactDetailComponent {
     this.sharedService.isMobileNavbarOpen = false;
   }
 
-  /**
-   * Converts a given timestamp to a human-readable date string.
-   * @param timestamp the timestamp to convert
-   * @returns a string in the format "DD. MMM. YYYY - HH:mm" in German or "MMM. DD, YYYY - hh:mm A" in English
-   */
-  convertTimestamp(timestamp: number) {
-    const date = new Date(timestamp);
-    const monthsEN = [
-      'Jan',
-      'Feb',
-      'Mar',
-      'Apr',
-      'May',
-      'Jun',
-      'Jul',
-      'Aug',
-      'Sep',
-      'Oct',
-      'Nov',
-      'Dec',
-    ];
-    const monthsDE = [
-      'Jan',
-      'Feb',
-      'Mär',
-      'Apr',
-      'Mai',
-      'Jun',
-      'Jul',
-      'Aug',
-      'Sep',
-      'Okt',
-      'Nov',
-      'Dez',
-    ];
-    const months =
-      this.languageService.currentLang === 'de' ? monthsDE : monthsEN;
-    const year = date.getFullYear();
-    const month = months[date.getMonth()];
-    const day = date.getDate();
-
-    if (this.languageService.currentLang === 'de') {
-      const time = `${day}. ${month}. ${year}`;
-      return `${time} - ${this.convertTimestampHourDE(timestamp)}`;
-    } else {
-      const time = `${month}. ${day}, ${year}`;
-      return `${time} - ${this.convertTimestampHourEN(timestamp)}`;
-    }
-  }
-
-  /**
-   * Converts a given timestamp to a human-readable time string in English.
-   * @param timestamp the timestamp to convert
-   * @returns a string in the format "hh:mm:ss AM/PM"
-   */
-  convertTimestampHourEN(timestamp: number) {
-    const date = new Date(timestamp * 1000);
-    let hour = date.getHours();
-    const minute = ('0' + date.getMinutes()).slice(-2);
-    const second = ('0' + date.getMinutes()).slice(-2);
-    const period = hour >= 12 ? 'PM' : 'AM';
-    hour = hour % 12 || 12;
-
-    let hourWithNull = ('0' + hour).slice(-2);
-
-    return `${hourWithNull}:${minute}:${second} ${period}`;
-  }
-
-  /**
-   * Converts a given timestamp to a human-readable time string in German.
-   *
-   * @param timestamp The timestamp to convert, in seconds.
-   * @returns A string in the format "HH:mm:ss Uhr".
-   */
-  convertTimestampHourDE(timestamp: number) {
-    const date = new Date(timestamp * 1000);
-    let hour = date.getHours();
-    const minute = ('0' + date.getMinutes()).slice(-2);
-    const second = ('0' + date.getMinutes()).slice(-2);
-
-    return `${hour}:${minute}:${second} Uhr`;
-  }
-
   @HostListener('document:click', ['$event'])
   /**
    * Handles the opening of the contact edit, new contact, and delete contact
diff --git a/src/app/components/contacts/contacts.component.html b/src/app/components/contacts/contacts.component.html
index 138dd9d..c4d704d 100644
--- a/src/app/components/contacts/contacts.component.html
+++ b/src/app/components/contacts/contacts.component.html
@@ -2,7 +2,7 @@
   <div
     class="left-frame"
     [ngClass]="{
-      'd-none': !showAllUsers && selectedUserId != undefined
+      'd-none': !showAllUsers && selectedUserId != null
     }"
   >
     <button class="btn-new" type="submit" (click)="openNewContactDialog()">
@@ -15,14 +15,14 @@
       </div>
     </button>
     <div class="content">
-      @for (sortLetter of this.sortFirstLetter(); track sortLetter) {
+      @for (sortLetter of this.getUniqueFirstLetters(); track sortLetter) {
       <div class="first-letter">{{ sortLetter }}</div>
       <div class="line"></div>
-      @for (user of this.sortUsersByFirstLetter(sortLetter); track user; let
+      @for (user of this.filterUsersByFirstLetter(sortLetter); track user; let
       index = $index) {
       <div
         class="contact"
-        (click)="showUserId(user.id)"
+        (click)="openUserDetails(user.id)"
         [ngClass]="{
           'contact-active': selectedUserId === user.id
         }"
@@ -67,7 +67,7 @@
   <div class="right-frame">
     <app-contact-detail
       [ngClass]="{
-        'd-none': !showAllUsers && selectedUserId == undefined
+        'd-none': !showAllUsers && selectedUserId == null
       }"
       [selectedUserId]="selectedUserId"
       [currentUser]="currentUser"
diff --git a/src/app/components/contacts/contacts.component.ts b/src/app/components/contacts/contacts.component.ts
index d0c810b..7974463 100644
--- a/src/app/components/contacts/contacts.component.ts
+++ b/src/app/components/contacts/contacts.component.ts
@@ -20,9 +20,7 @@ import { finalize } from 'rxjs';
 export class ContactsComponent {
   allUsers: User[] = [];
   currentUser: User | null = null;
-  selectedUserId: string | undefined;
-  usersFirstLetter: string[] = [];
-  usersByFirstLetter: { [key: string]: string[] } = {};
+  selectedUserId: string | null = null;
   showAllUsers: boolean = false;
   isLoading: boolean = false;
 
@@ -41,23 +39,6 @@ export class ContactsComponent {
     this.loadCurrentUser();
   }
 
-  @HostListener('window:resize', ['$event'])
-  /**
-   * Toggles the showAllUsers variable based on the window width and the
-   * currentUserId of the shared service.
-   *
-   * If the window width is less than or equal to 1150px and the currentUserId
-   * is not empty, showAllUsers is set to false. Otherwise, showAllUsers is set
-   * to true.
-   */
-  onResize() {
-    if (window.innerWidth <= 1150 && this.selectedUserId != undefined) {
-      this.showAllUsers = false;
-    } else {
-      this.showAllUsers = true;
-    }
-  }
-
   loadAllUsers(): void {
     this.isLoading = true;
 
@@ -85,7 +66,7 @@ export class ContactsComponent {
    * If the parameter is not given, it resets the current user id to an empty string.
    * @param userId - the id of the user to be set as the current user id
    */
-  showUserId(userId: string = '') {
+  openUserDetails(userId: string = '') {
     this.selectedUserId = userId;
     this.onResize();
   }
@@ -94,37 +75,24 @@ export class ContactsComponent {
    * Triggers the resize function to adjust UI elements based on the current state.
    */
   closeContactEmitter() {
-    this.selectedUserId = undefined;
+    this.selectedUserId = null;
     this.onResize();
   }
 
-  /**
-   * Sorts the users array by the first letter of the user's initials, and filters it by the given sort letter.
-   * @param sortLetter - the letter to filter the users by
-   * @returns An array of users with the given sort letter
-   */
-  sortUsersByFirstLetter(sortLetter: string) {
+  filterUsersByFirstLetter(filterLetter: string) {
     return this.allUsers.filter(
-      (user) => user.initials.substring(0, 1) === sortLetter
+      (user) => user.initials.substring(0, 1) === filterLetter
     );
   }
 
-  /**
-   * Returns an array of unique first letters from the sorted array of users.
-   * The users array is first sorted by the first letter of the user's first name,
-   * and then the first letter of each user's first name is extracted and
-   * converted to uppercase. The resulting array is then deduplicated with a
-   * Set, and the unique letters are returned in an array.
-   * @returns An array of unique first letters
-   */
-  sortFirstLetter() {
-    let filterteArray = this.allUsers.sort((a, b) =>
+  getUniqueFirstLetters() {
+    let sortedUsers = this.allUsers.sort((a, b) =>
       a.firstName.localeCompare(b.firstName)
     );
-    let usersFirstLetter = Array.from(
-      new Set(filterteArray.map((user) => user.firstName[0].toUpperCase()))
+    let uniqueFirstLetters = Array.from(
+      new Set(sortedUsers.map((user) => user.firstName[0].toUpperCase()))
     );
-    return usersFirstLetter;
+    return uniqueFirstLetters;
   }
 
   /**
@@ -137,4 +105,13 @@ export class ContactsComponent {
     this.sharedService.isAnyDialogOpen = true;
     this.sharedService.isNewContactDialogOpen = true;
   }
+
+  @HostListener('window:resize', ['$event'])
+  onResize() {
+    if (window.innerWidth <= 1150 && this.selectedUserId != undefined) {
+      this.showAllUsers = false;
+    } else {
+      this.showAllUsers = true;
+    }
+  }
 }