diff --git a/index.html b/index.html
index d90dec83..f2d7a261 100644
--- a/index.html
+++ b/index.html
@@ -29,46 +29,5 @@
                 }
             });
 		</script>
-        <script id="service-worker" type="module">
-
-            function workerMessage(worker, type) {
-                const body = {type, id: Math.floor(Math.random() * Number.MAX_SAFE_INTEGER)};
-                let resolve;
-                const promise = new Promise(r => resolve = r);
-                const onMessage = function(event) {
-                    if (event.data.replyTo === body.id) {
-                        navigator.serviceWorker.removeEventListener("message", onMessage);
-                        resolve(event.data.content);
-                    }
-                }
-                navigator.serviceWorker.addEventListener("message", onMessage);
-                worker.postMessage(body);
-                return promise;
-            }
-
-            if('serviceWorker' in navigator) {
-                navigator.serviceWorker.register('sw.js').then(function(registration) {
-                    console.log("Service Worker registered");
-                    async function tryActivateUpdate() {
-                        if (registration.waiting && registration.active) {
-                            const version = await workerMessage(registration.waiting, "version");
-                            if (confirm(`Version ${version.version} (${version.buildHash}) is ready to install. Apply now?`)) {
-                                registration.waiting.postMessage({type: "skipWaiting"}); // will trigger controllerchange event
-                            }
-                        }
-                    }
-                    tryActivateUpdate();
-                    registration.onupdatefound = function() {
-                        const newWorker = registration.installing;
-                        newWorker.onstatechange = function() {
-                            tryActivateUpdate();
-                        }
-                    };
-                });
-                navigator.serviceWorker.addEventListener("controllerchange", function() {
-                    document.location.reload();
-                });
-            }
-        </script>
 	</body>
 </html>
diff --git a/scripts/build.mjs b/scripts/build.mjs
index 81399039..1534fc7a 100644
--- a/scripts/build.mjs
+++ b/scripts/build.mjs
@@ -140,6 +140,7 @@ async function buildHtml(doc, version, globalHash, modernOnly, assets) {
     });
     const pathsJSON = JSON.stringify({
         worker: assets.has("worker.js") ? assets.resolve(`worker.js`) : null,
+        serviceWorker: "sw.js",
         olm: {
             wasm: assets.resolve("olm.wasm"),
             legacyBundle: assets.resolve("olm_legacy.js"),
@@ -156,7 +157,6 @@ async function buildHtml(doc, version, globalHash, modernOnly, assets) {
         );
     }
     doc("script#main").replaceWith(mainScripts.join(""));
-    doc("script#service-worker").attr("type", "text/javascript");
 
     const versionScript = doc("script#version");
     versionScript.attr("type", "text/javascript");
diff --git a/src/main.js b/src/main.js
index d98448dd..792c333b 100644
--- a/src/main.js
+++ b/src/main.js
@@ -25,6 +25,7 @@ import {RootViewModel} from "./domain/RootViewModel.js";
 import {createNavigation, createRouter} from "./domain/navigation/index.js";
 import {RootView} from "./ui/web/RootView.js";
 import {Clock} from "./ui/web/dom/Clock.js";
+import {ServiceWorkerHandler} from "./ui/web/dom/ServiceWorkerHandler.js";
 import {History} from "./ui/web/dom/History.js";
 import {OnlineStatus} from "./ui/web/dom/OnlineStatus.js";
 import {CryptoDriver} from "./ui/web/dom/CryptoDriver.js";
@@ -106,8 +107,14 @@ export async function main(container, paths, legacyExtras) {
         } else {
             request = xhrRequest;
         }
+        const navigation = createNavigation();
         const sessionInfoStorage = new SessionInfoStorage("hydrogen_sessions_v1");
-        const storageFactory = new StorageFactory();
+        let serviceWorkerHandler;
+        if (paths.serviceWorker && "serviceWorker" in navigator) {
+            serviceWorkerHandler = new ServiceWorkerHandler({navigation});
+            serviceWorkerHandler.registerAndStart(paths.serviceWorker);
+        }
+        const storageFactory = new StorageFactory(serviceWorkerHandler);
 
         const olmPromise = loadOlm(paths.olm);
         // if wasm is not supported, we'll want
@@ -116,8 +123,6 @@ export async function main(container, paths, legacyExtras) {
         if (!window.WebAssembly) {
             workerPromise = loadOlmWorker(paths);
         }
-
-        const navigation = createNavigation();
         const urlRouter = createRouter({navigation, history: new History()});
         urlRouter.attach();
 
@@ -139,7 +144,8 @@ export async function main(container, paths, legacyExtras) {
             storageFactory,
             clock,
             urlRouter,
-            navigation
+            navigation,
+            updateService: serviceWorkerHandler
         });
         window.__brawlViewModel = vm;
         await vm.load();
diff --git a/src/ui/web/dom/ServiceWorkerHandler.js b/src/ui/web/dom/ServiceWorkerHandler.js
new file mode 100644
index 00000000..e76f202c
--- /dev/null
+++ b/src/ui/web/dom/ServiceWorkerHandler.js
@@ -0,0 +1,150 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// 3 (imaginary) interfaces are implemented here:
+// - OfflineAvailability (done by registering the sw)
+// - UpdateService (see checkForUpdate method, and should also emit events rather than showing confirm dialog here)
+// - ConcurrentAccessBlocker (see preventConcurrentSessionAccess method)
+export class ServiceWorkerHandler {
+    constructor({navigation}) {
+        this._waitingForReply = new Map();
+        this._messageIdCounter = 0;
+        this._registration = null;
+        this._navigation = navigation;
+        this._registrationPromise = null;
+    }
+
+    registerAndStart(path) {
+        this._registrationPromise = (async () => {
+            navigator.serviceWorker.addEventListener("message", this);
+            navigator.serviceWorker.addEventListener("controllerchange", this);
+            this._registration = await navigator.serviceWorker.register(path);
+            this._registrationPromise = null;
+            console.log("Service Worker registered");
+            this._registration.addEventListener("updatefound", this);
+            this._tryActivateUpdate();
+        })();
+    }
+
+    _onMessage(event) {
+        const {data} = event;
+        const replyTo = data.replyTo;
+        if (replyTo) {
+            const resolve = this._waitingForReply.get(replyTo);
+            if (resolve) {
+                this._waitingForReply.delete(replyTo);
+                resolve(data.payload);
+            }
+        }
+        if (data.type === "closeSession") {
+            const {sessionId} = data.payload;
+            this._closeSessionIfNeeded(sessionId).finally(() => {
+                event.source.postMessage({replyTo: data.id});
+            });
+        }
+    }
+
+    _closeSessionIfNeeded(sessionId) {
+        const currentSession = this._navigation.path.get("session");
+        if (sessionId && currentSession?.value === sessionId) {
+            return new Promise(resolve => {
+                const unsubscribe = this._navigation.pathObservable.subscribe(path => {
+                    const session = path.get("session");
+                    if (!session || session.value !== sessionId) {
+                        unsubscribe();
+                        resolve();
+                    }
+                });
+                this._navigation.push("session");
+            });
+        } else {
+            return Promise.resolve();
+        }
+    }
+
+    async _tryActivateUpdate() {
+        if (this._registration.waiting && this._registration.active) {
+            this._registration.waiting.removeEventListener("statechange", this);
+            const version = await this._sendAndWaitForReply("version", null, this._registration.waiting);
+            if (confirm(`Version ${version.version} (${version.buildHash}) is ready to install. Apply now?`)) {
+                this._registration.waiting.postMessage({type: "skipWaiting"}); // will trigger controllerchange event
+            }
+        }
+    }
+
+    handleEvent(event) {
+        switch (event.type) {
+            case "message":
+                this._onMessage(event);
+                break;
+            case "updatefound":
+                this._registration.installing.addEventListener("statechange", this);
+                this._tryActivateUpdate();
+                break;
+            case "statechange":
+                this._tryActivateUpdate();
+                break;
+            case "controllerchange":
+                // active service worker changed,
+                // refresh, so we can get all assets 
+                // (and not some if we would not refresh)
+                // up to date from it
+                document.location.reload();
+                break;
+        }
+    }
+
+    async _send(type, payload, worker = undefined) {
+        if (this._registrationPromise) {
+            await this._registrationPromise;
+        }
+        if (!worker) {
+            worker = this._registration.active;
+        }
+        worker.postMessage({type, payload});
+    }
+
+    async _sendAndWaitForReply(type, payload, worker = undefined) {
+        if (this._registrationPromise) {
+            await this._registrationPromise;
+        }
+        if (!worker) {
+            worker = this._registration.active;
+        }
+        this._messageIdCounter += 1;
+        const id = this._messageIdCounter;
+        const promise = new Promise(resolve => {
+            this._waitingForReply.set(id, resolve);
+        });
+        worker.postMessage({type, id, payload});
+        return await promise;
+    }
+
+    async checkForUpdate() {
+        if (this._registrationPromise) {
+            await this._registrationPromise;
+        }
+        this._registration.update();
+    }
+
+    async preventConcurrentSessionAccess(sessionId) {
+        // don't block if we didn't manage to install service worker
+        if (!this._registration) {
+            return Promise.resolve();
+        }
+        return this._sendAndWaitForReply("closeSession", {sessionId});
+    }
+}