diff --git a/src/app/mirror_ui.rs b/src/app/mirror_ui.rs
index 724e615..6708af2 100644
--- a/src/app/mirror_ui.rs
+++ b/src/app/mirror_ui.rs
@@ -762,6 +762,8 @@ impl App {
         self.mir.base = Value::Null;
         self.mir.local = Some(local);
         self.mir.on = true;
+        // The bots' computer is the brain's now; this one's box isn't kept awake.
+        crate::cloudbox::set_brain(false);
         self.mir.online = false;
         self.mir.version.store(0, Ordering::SeqCst);
         self.mir.pending.lock().unwrap().clear();
@@ -777,6 +779,7 @@ impl App {
     fn mirror_leave(&mut self) {
         self.mir.gen.fetch_add(1, Ordering::SeqCst);
         self.mir.on = false;
+        crate::cloudbox::set_brain(true);
         self.mir.online = false;
         self.mir.outbox = None;
         self.streams.clear();
diff --git a/src/cloudbox.rs b/src/cloudbox.rs
index 25d94f6..10540a9 100644
--- a/src/cloudbox.rs
+++ b/src/cloudbox.rs
@@ -697,12 +697,14 @@ pub fn start_background() {
         set_run(probe());
         resume_interrupted();
         loop {
+            // (First wait a little: a computer showing another brain says so right after start.)
+            std::thread::sleep(Duration::from_secs(20));
             let (idle, rebuilding) = {
                 let s = shared().lock().unwrap();
                 (s.last_used.elapsed().as_secs(), s.rebuilding)
             };
             if !rebuilding {
-                if matches!(probe(), Run::Asleep) {
+                if IS_BRAIN.load(Ordering::SeqCst) && matches!(probe(), Run::Asleep) {
                     log("Bot 的電腦不休眠：叫醒它。");
                     let _ = ensure_running();
                 }
@@ -714,11 +716,17 @@ pub fn start_background() {
                 refresh();
                 maybe_scheduled_update();
             }
-            std::thread::sleep(Duration::from_secs(20));
         }
     });
 }
 
+/// This AnyBot is the brain (its box is the bots' computer). A computer showing another brain
+/// doesn't use its own box, so it isn't kept awake there.
+static IS_BRAIN: AtomicBool = AtomicBool::new(true);
+pub fn set_brain(on: bool) {
+    IS_BRAIN.store(on, Ordering::SeqCst);
+}
+
 static VIEWER_OPEN: AtomicBool = AtomicBool::new(false);
 pub fn set_viewer_open(on: bool) {
     VIEWER_OPEN.store(on, Ordering::SeqCst);