diff --git a/watchers/src/report_client.rs b/watchers/src/report_client.rs
index fb2fcf7..aa5fb44 100644
--- a/watchers/src/report_client.rs
+++ b/watchers/src/report_client.rs
@@ -4,6 +4,7 @@ use anyhow::Context;
 use aw_client_rust::{AwClient, Event as AwEvent};
 use chrono::{DateTime, TimeDelta, Utc};
 use serde_json::{Map, Value};
+use std::collections::HashMap;
 use std::error::Error;
 use std::future::Future;
 
@@ -93,6 +94,16 @@ impl ReportClient {
     }
 
     pub async fn send_active_window(&self, app_id: &str, title: &str) -> anyhow::Result<()> {
+        self.send_active_window_with_extra(app_id, title, None)
+            .await
+    }
+
+    pub async fn send_active_window_with_extra(
+        &self,
+        app_id: &str,
+        title: &str,
+        extra_data: Option<HashMap<String, String>>,
+    ) -> anyhow::Result<()> {
         let mut data = Map::new();
 
         if let Some((inserted_app_id, inserted_title)) = self.get_filtered_data(app_id, title) {
@@ -104,6 +115,12 @@ impl ReportClient {
 
             data.insert("app".to_string(), Value::String(inserted_app_id));
             data.insert("title".to_string(), Value::String(inserted_title));
+
+            if let Some(extra) = extra_data {
+                for (key, value) in extra {
+                    data.insert(key, Value::String(value));
+                }
+            }
         } else {
             return Ok(());
         }
diff --git a/watchers/src/watchers/x11_connection.rs b/watchers/src/watchers/x11_connection.rs
index 91244cc..173591d 100644
--- a/watchers/src/watchers/x11_connection.rs
+++ b/watchers/src/watchers/x11_connection.rs
@@ -9,6 +9,7 @@ use x11rb::rust_connection::RustConnection;
 pub struct WindowData {
     pub title: String,
     pub app_id: String,
+    pub wm_instance: String,
 }
 
 pub struct X11Client {
@@ -86,10 +87,12 @@ impl X11Client {
             )?;
 
             let title = str::from_utf8(&name.value).with_context(|| "Invalid title UTF")?;
+            let (instance, class) = parse_wm_class(&class)?;
 
             Ok(WindowData {
                 title: title.to_string(),
-                app_id: parse_wm_class(&class)?.to_string(),
+                app_id: class,
+                wm_instance: instance,
             })
         })
     }
@@ -149,21 +152,26 @@ impl X11Client {
     }
 }
 
-fn parse_wm_class(property: &GetPropertyReply) -> anyhow::Result<&str> {
+fn parse_wm_class(property: &GetPropertyReply) -> anyhow::Result<(String, String)> {
     if property.format != 8 {
         bail!("Malformed property: wrong format");
     }
     let value = &property.value;
     // The property should contain two null-terminated strings. Find them.
     if let Some(middle) = value.iter().position(|&b| b == 0) {
-        let (_, class) = value.split_at(middle);
-        // Skip the null byte at the beginning
+        let (instance, class) = value.split_at(middle);
+        // Remove the null byte at the end of the instance
+        let instance = &instance[..instance.len()];
+        // Skip the null byte at the beginning of the class
         let mut class = &class[1..];
         // Remove the last null byte from the class, if it is there.
         if class.last() == Some(&0) {
             class = &class[..class.len() - 1];
         }
-        Ok(std::str::from_utf8(class)?)
+        Ok((
+            std::str::from_utf8(instance)?.to_string(),
+            std::str::from_utf8(class)?.to_string(),
+        ))
     } else {
         bail!("Missing null byte")
     }
diff --git a/watchers/src/watchers/x11_window.rs b/watchers/src/watchers/x11_window.rs
index 3776a72..1534a6e 100644
--- a/watchers/src/watchers/x11_window.rs
+++ b/watchers/src/watchers/x11_window.rs
@@ -2,31 +2,55 @@ use super::{x11_connection::X11Client, Watcher};
 use crate::report_client::ReportClient;
 use anyhow::Context;
 use async_trait::async_trait;
+use std::collections::HashMap;
 use std::sync::Arc;
 
 pub struct WindowWatcher {
     client: X11Client,
-    last_title: String,
     last_app_id: String,
+    last_title: String,
+    last_wm_instance: String,
 }
 
 impl WindowWatcher {
+    pub async fn send_active_window_with_instance(
+        &self,
+        client: &ReportClient,
+        app_id: &str,
+        title: &str,
+        wm_instance: &str,
+    ) -> anyhow::Result<()> {
+        let mut extra_data = HashMap::new();
+        extra_data.insert("wm_instance".to_string(), wm_instance.to_string());
+        client
+            .send_active_window_with_extra(app_id, title, Some(extra_data))
+            .await
+    }
+
     async fn send_active_window(&mut self, client: &ReportClient) -> anyhow::Result<()> {
         let data = self.client.active_window_data()?;
 
-        if data.app_id != self.last_app_id || data.title != self.last_title {
+        if data.app_id != self.last_app_id
+            || data.title != self.last_title
+            || data.wm_instance != self.last_wm_instance
+        {
             debug!(
-                r#"Changed window app_id="{}", title="{}""#,
-                data.app_id, data.title
+                r#"Changed window app_id="{}", title="{}", wm_instance="{}""#,
+                data.app_id, data.title, data.wm_instance
             );
-            self.last_app_id = data.app_id;
-            self.last_title = data.title;
+            self.last_app_id = data.app_id.clone();
+            self.last_title = data.title.clone();
+            self.last_wm_instance = data.wm_instance.clone();
         }
 
-        client
-            .send_active_window(&self.last_app_id, &self.last_title)
-            .await
-            .with_context(|| "Failed to send heartbeat for active window")
+        self.send_active_window_with_instance(
+            client,
+            &self.last_app_id,
+            &self.last_title,
+            &self.last_wm_instance,
+        )
+        .await
+        .with_context(|| "Failed to send heartbeat for active window")
     }
 }
 
@@ -40,6 +64,7 @@ impl Watcher for WindowWatcher {
             client,
             last_title: String::new(),
             last_app_id: String::new(),
+            last_wm_instance: String::new(),
         })
     }