diff --git a/src/UserActivity.js b/src/UserActivity.js
index 8b136c0bcc..669b007934 100644
--- a/src/UserActivity.js
+++ b/src/UserActivity.js
@@ -16,7 +16,8 @@ limitations under the License.
 
 var dis = require("./dispatcher");
 
-var MIN_DISPATCH_INTERVAL = 1 * 1000;
+var MIN_DISPATCH_INTERVAL_MS = 500;
+var CURRENTLY_ACTIVE_THRESHOLD_MS = 500;
 
 /**
  * This class watches for user activity (moving the mouse or pressing a key)
@@ -38,6 +39,7 @@ class UserActivity {
         window.addEventListener('wheel', this._onUserActivity.bind(this), true);
         this.lastActivityAtTs = new Date().getTime();
         this.lastDispatchAtTs = 0;
+        this.activityEndTimer = undefined;
     }
 
     /**
@@ -49,6 +51,14 @@ class UserActivity {
         window.removeEventListener('wheel', this._onUserActivity.bind(this), true);
     }
 
+    /**
+     * Return true if there has been user activity very recently
+     * (ie. within a few seconds)
+     */
+    userCurrentlyActive() {
+        return this.lastActivityAtTs > new Date().getTime() - CURRENTLY_ACTIVE_THRESHOLD_MS;
+    }
+
     _onUserActivity(event) {
         if (event.screenX && event.type == "mousemove") {
             if (event.screenX === this.lastScreenX &&
@@ -61,12 +71,32 @@ class UserActivity {
             this.lastScreenY = event.screenY;
         }
 
-        this.lastActivityAtTs = (new Date).getTime();
-        if (this.lastDispatchAtTs < this.lastActivityAtTs - MIN_DISPATCH_INTERVAL) {
+        this.lastActivityAtTs = new Date().getTime();
+        if (this.lastDispatchAtTs < this.lastActivityAtTs - MIN_DISPATCH_INTERVAL_MS) {
             this.lastDispatchAtTs = this.lastActivityAtTs;
             dis.dispatch({
                 action: 'user_activity'
             });
+            if (!this.activityEndTimer) {
+                this.activityEndTimer = setTimeout(
+                    this._onActivityEndTimer.bind(this), MIN_DISPATCH_INTERVAL_MS
+                );
+            }
+        }
+    }
+
+    _onActivityEndTimer() {
+        var now = new Date().getTime();
+        var targetTime = this.lastActivityAtTs + MIN_DISPATCH_INTERVAL_MS;
+        if (now >= targetTime) {
+            dis.dispatch({
+                action: 'user_activity_end'
+            });
+            this.activityEndTimer = undefined;
+        } else {
+            this.activityEndTimer = setTimeout(
+                this._onActivityEndTimer.bind(this), targetTime - now
+            );
         }
     }
 }
diff --git a/src/components/structures/RoomView.js b/src/components/structures/RoomView.js
index 8e193b25ab..842bb1273d 100644
--- a/src/components/structures/RoomView.js
+++ b/src/components/structures/RoomView.js
@@ -220,6 +220,12 @@ module.exports = React.createClass({
 
                 break;
             case 'user_activity':
+            case 'user_activity_end':
+                // we could treat user_activity_end differently and not
+                // send receipts for messages that have arrived between
+                // the actual user activity and the time they stopped
+                // being active, but let's see if this is actually
+                // necessary.
                 this.sendReadReceipt();
                 break;
         }