diff --git a/specs/001-modbus-relay-control/tasks.org b/specs/001-modbus-relay-control/tasks.org
index b82d16e..826ab75 100644
--- a/specs/001-modbus-relay-control/tasks.org
+++ b/specs/001-modbus-relay-control/tasks.org
@@ -891,8 +891,8 @@ CLOSED: [2026-05-14 jeu. 20:09]
   - *File*: =src/presentation/api/relay_api.rs=
   - *Complexity*: Low | *Uncertainty*: Low
 
-*** TODO Frontend Implementation [0/2]
-- [ ] *T052* [P] [US1] [TDD] Create =RelayDto= TypeScript interface
+*** TODO Frontend Implementation [1/2]
+- [X] *T052* [P] [US1] [TDD] Create =RelayDto= TypeScript interface
   - Generate from OpenAPI spec or manually define
   - *File*: =frontend/src/types/relay.ts=
   - *Complexity*: Low | *Uncertainty*: Low
diff --git a/src/composables/useRelay.ts b/src/composables/useRelay.ts
new file mode 100644
index 0000000..e62e4e9
--- /dev/null
+++ b/src/composables/useRelay.ts
@@ -0,0 +1,37 @@
+import { ref } from 'vue';
+import { apiClient } from '../api/client';
+import { relayDtoToDomain } from '../types/mappers/relayDtoMapper';
+import type { Relay, RelayDto } from '../types/relay';
+
+export function useRelay() {
+  const isLoading = ref(false);
+  const error = ref<string | null>(null);
+  const response = ref<Relay | null>(null);
+
+  const toggleRelay = async (id: number) => {
+    isLoading.value = true;
+    try {
+      const { data } = await apiClient.POST('/api/relays/{id}/toggle', {
+        params: {
+          path: {
+            id,
+          },
+        },
+      });
+      error.value = null;
+      response.value = relayDtoToDomain(data as RelayDto);
+    } catch (err: any) {
+      console.error(`Failed to toggle relay ${id}:`, err);
+      error.value = err.message || `Failed to toggle relay ${id}`;
+    } finally {
+      isLoading.value = false;
+    }
+  };
+
+  return {
+    toggleRelay,
+    isLoading,
+    error,
+    response,
+  };
+}
diff --git a/src/composables/useRelayPolling.ts b/src/composables/useRelayPolling.ts
new file mode 100644
index 0000000..3a5e8c9
--- /dev/null
+++ b/src/composables/useRelayPolling.ts
@@ -0,0 +1,51 @@
+import { onMounted, onUnmounted, ref } from 'vue';
+
+import { apiClient } from '../api/client';
+import { relayDtoToDomain } from '../types/mappers/relayDtoMapper';
+import type { Relay } from '../types/relay';
+import { isNil } from '../utils/isNil';
+
+export function useRelayPolling(intervalMs: number = 2000) {
+  const relays = ref<Relay[]>([]);
+  const isLoading = ref(false);
+  const error = ref<string | null>(null);
+
+  let pollingInterval: number | null = null;
+
+  const fetchData = async () => {
+    isLoading.value = true;
+    try {
+      const { data } = await apiClient.GET('/api/relays');
+      relays.value = data?.map(relayDtoToDomain) ?? [];
+      error.value = null;
+    } catch (err: any) {
+      console.error('Polling error:', err);
+      error.value = err.message || 'Failed to fetch data';
+    } finally {
+      isLoading.value = false;
+    }
+  };
+
+  const startPolling = () => {
+    fetchData();
+    pollingInterval = window.setInterval(fetchData, intervalMs);
+  };
+
+  const stopPolling = () => {
+    if (isNil(pollingInterval)) {
+      return;
+    }
+    clearInterval(pollingInterval);
+    pollingInterval = null;
+  };
+
+  onMounted(startPolling);
+  onUnmounted(stopPolling);
+
+  return {
+    relays,
+    isLoading,
+    error,
+    refresh: fetchData,
+  };
+}
diff --git a/src/main.ts b/src/main.ts
index 3c9bfeb..3a0e429 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,5 +1,6 @@
-import { createApp } from "vue";
-import "./style.css";
-import App from "./App.vue";
+import { createApp } from 'vue';
 
-createApp(App).mount("#app");
+import './style.css';
+import App from './App.vue';
+
+createApp(App).mount('#app');
diff --git a/src/types/mappers/relayDtoMapper.ts b/src/types/mappers/relayDtoMapper.ts
new file mode 100644
index 0000000..6a5157c
--- /dev/null
+++ b/src/types/mappers/relayDtoMapper.ts
@@ -0,0 +1,13 @@
+import { isNil } from '../../utils/isNil';
+import { RelayState, Relay, type RelayDto } from '../relay';
+
+const relayStateToDomain = (dto: string | null): RelayState => {
+  if (isNil(dto) || dto.trim() === '') {
+    return RelayState.Off;
+  }
+  return dto.trim().toLowerCase() === 'on' ? RelayState.On : RelayState.Off;
+};
+
+export const relayDtoToDomain = (dto: RelayDto): Relay => {
+  return new Relay(dto.id, relayStateToDomain(dto.state), dto.label);
+};
diff --git a/src/types/relay.ts b/src/types/relay.ts
new file mode 100644
index 0000000..3b595da
--- /dev/null
+++ b/src/types/relay.ts
@@ -0,0 +1,20 @@
+import type { components } from '../api/schema';
+
+export type RelayDto = components['schemas']['RelayDto'];
+
+export enum RelayState {
+  On = 'on',
+  Off = 'off',
+}
+
+export class Relay {
+  id: number;
+  state: RelayState;
+  label: string;
+
+  constructor(id: number, state: RelayState, label: string) {
+    this.id = id;
+    this.state = state;
+    this.label = label;
+  }
+}
diff --git a/src/utils/isNil.ts b/src/utils/isNil.ts
new file mode 100644
index 0000000..bd50ad1
--- /dev/null
+++ b/src/utils/isNil.ts
@@ -0,0 +1,2 @@
+export const isNil = (value: unknown | null | undefined): value is null | undefined =>
+  value === null || value === undefined;
diff --git a/tsconfig.app.json b/tsconfig.app.json
index 8d16e42..24fca7a 100644
--- a/tsconfig.app.json
+++ b/tsconfig.app.json
@@ -8,9 +8,10 @@
     "strict": true,
     "noUnusedLocals": true,
     "noUnusedParameters": true,
-    "erasableSyntaxOnly": true,
+    "erasableSyntaxOnly": false,
     "noFallthroughCasesInSwitch": true,
-    "noUncheckedSideEffectImports": true
+    "noUncheckedSideEffectImports": true,
+    "noUncheckedIndexedAccess": true,
   },
   "include": ["src/**/*.ts", "src/**/*.tsx", "src/**/*.vue"]
 }
diff --git a/tsconfig.node.json b/tsconfig.node.json
index 8a67f62..62eb1d4 100644
--- a/tsconfig.node.json
+++ b/tsconfig.node.json
@@ -18,9 +18,10 @@
     "strict": true,
     "noUnusedLocals": true,
     "noUnusedParameters": true,
-    "erasableSyntaxOnly": true,
+    "erasableSyntaxOnly": false,
     "noFallthroughCasesInSwitch": true,
-    "noUncheckedSideEffectImports": true
+    "noUncheckedSideEffectImports": true,
+    "noUncheckedIndexedAccess": true,
   },
   "include": ["vite.config.ts"]
 }