diff --git a/docs/module_reference.md b/docs/module_reference.md
index 68f60230..3805690b 100644
--- a/docs/module_reference.md
+++ b/docs/module_reference.md
@@ -653,6 +653,10 @@ The `disconnect()` method might be useful to access the other microcontroller on
 
 Note that the expander forwards all other method calls to the remote core module, e.g. `expander.info()`.
 
+| Properties         | Description                                             | Data type |
+| ------------------ | ------------------------------------------------------- | --------- |
+| `last_message_age` | Time since last message from other microcontroller (ms) | `int`     |
+
 ## Proxy
 
 -- _This module is mainly for internal use with the expander module._ --
diff --git a/main/modules/expander.cpp b/main/modules/expander.cpp
index 70660841..ba3c8bf0 100644
--- a/main/modules/expander.cpp
+++ b/main/modules/expander.cpp
@@ -12,6 +12,8 @@ Expander::Expander(const std::string name,
                    const gpio_num_t enable_pin,
                    MessageHandler message_handler)
     : Module(expander, name), serial(serial), boot_pin(boot_pin), enable_pin(enable_pin), message_handler(message_handler) {
+    this->properties["last_message_age"] = std::make_shared<IntegerVariable>();
+
     serial->enable_line_detection();
     if (boot_pin != GPIO_NUM_NC && enable_pin != GPIO_NUM_NC) {
         gpio_reset_pin(boot_pin);
@@ -45,13 +47,14 @@ void Expander::step() {
     while (this->serial->has_buffered_lines()) {
         int len = this->serial->read_line(buffer);
         check(buffer, len);
+        this->last_message_millis = millis();
         if (buffer[0] == '!' && buffer[1] == '!') {
-            /* Don't trigger keep-alive from expander updates */
-            this->message_handler(&buffer[2], false, true);
+            this->message_handler(&buffer[2], false, true); // Don't trigger core keep-alive from expander broadcasts
         } else {
             echo("%s: %s", this->name.c_str(), buffer);
         }
     }
+    this->properties.at("last_message_age")->integer_value = millis_since(this->last_message_millis);
     Module::step();
 }
 
diff --git a/main/modules/expander.h b/main/modules/expander.h
index dd88d05a..c86d6f65 100644
--- a/main/modules/expander.h
+++ b/main/modules/expander.h
@@ -8,6 +8,9 @@ class Expander;
 using Expander_ptr = std::shared_ptr<Expander>;
 
 class Expander : public Module {
+private:
+    unsigned long int last_message_millis = 0;
+
 public:
     const ConstSerial_ptr serial;
     const gpio_num_t boot_pin;