diff --git a/src/main.rs b/src/main.rs
index 8006681..963dc85 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -18,6 +18,7 @@ use daemonize::Daemonize;
 use serialport;
 
 use std::{
+    env,
     fs,
     path::Path,
     sync::{mpsc, Arc, Mutex},
@@ -74,6 +75,28 @@ fn ensure_config() {
 }
 
 fn find_serial_port() -> Option<String> {
+    // Prefer environment variable if provided (e.g., by entrypoint for mock PTY)
+    if let Ok(path) = env::var("HACI_SERIAL_PORT") {
+        let p = Path::new(&path);
+        if !p.exists() {
+            // Wait up to ~5 seconds for the PTY to appear
+            for _ in 0..50 {
+                if p.exists() {
+                    break;
+                }
+                thread::sleep(std::time::Duration::from_millis(100));
+            }
+        }
+        if p.exists() {
+            return Some(path);
+        } else {
+            log::warn!(
+                "HACI_SERIAL_PORT='{}' does not exist. Falling back to port scan.",
+                path
+            );
+        }
+    }
+
     if let Ok(ports) = serialport::available_ports() {
         for p in ports {
             if p.port_name.starts_with("/dev/ttyACM")
@@ -172,7 +195,7 @@ async fn main() {
     let serial_port_path = match find_serial_port() {
         Some(port) => port,
         None => {
-            log::error!("❌ No serial port found. Please connect the Teensy device.");
+            log::error!("❌ No serial port found. Set HACI_SERIAL_PORT to a device path (e.g., /dev/ttyACM0) or connect the Teensy device.");
             return;
         }
     };