diff --git a/packages/cli-v3/src/commands/dev.ts b/packages/cli-v3/src/commands/dev.ts
index b6c652d786..8634ad422d 100644
--- a/packages/cli-v3/src/commands/dev.ts
+++ b/packages/cli-v3/src/commands/dev.ts
@@ -11,6 +11,7 @@ import { runtimeChecks } from "../utilities/runtimeCheck.js";
 import { getProjectClient, LoginResultOk } from "../utilities/session.js";
 import { login } from "./login.js";
 import { updateTriggerPackages } from "./update.js";
+import { createLockFile } from "../dev/lock.js";
 
 const DevCommandOptions = CommonCommandOptions.extend({
   debugOtel: z.boolean().default(false),
@@ -120,6 +121,8 @@ async function startDev(options: StartDevOptions) {
       displayedUpdateMessage = await updateTriggerPackages(options.cwd, { ...options }, true, true);
     }
 
+    const removeLockFile = await createLockFile(options.cwd);
+
     let devInstance: DevSessionInstance | undefined;
 
     printDevBanner(displayedUpdateMessage);
@@ -178,6 +181,7 @@ async function startDev(options: StartDevOptions) {
       stop: async () => {
         devInstance?.stop();
         await watcher?.stop();
+        removeLockFile();
       },
       waitUntilExit,
     };
diff --git a/packages/cli-v3/src/dev/lock.ts b/packages/cli-v3/src/dev/lock.ts
new file mode 100644
index 0000000000..602607a4c0
--- /dev/null
+++ b/packages/cli-v3/src/dev/lock.ts
@@ -0,0 +1,93 @@
+import path from "node:path";
+import { readFile } from "../utilities/fileSystem.js";
+import { tryCatch } from "@trigger.dev/core/utils";
+import { logger } from "../utilities/logger.js";
+import { mkdir, writeFile } from "node:fs/promises";
+import { existsSync, unlinkSync } from "node:fs";
+import { onExit } from "signal-exit";
+
+const LOCK_FILE_NAME = "dev.lock";
+
+export async function createLockFile(cwd: string) {
+  const currentPid = process.pid;
+  const lockFilePath = path.join(cwd, ".trigger", LOCK_FILE_NAME);
+
+  logger.debug("Checking for lockfile", { lockFilePath, currentPid });
+
+  const removeLockFile = () => {
+    try {
+      logger.debug("Removing lockfile", { lockFilePath });
+      return unlinkSync(lockFilePath);
+    } catch (e) {
+      // This sometimes fails on Windows with EBUSY
+    }
+  };
+  const removeExitListener = onExit(removeLockFile);
+
+  const [, existingLockfileContents] = await tryCatch(readFile(lockFilePath));
+
+  if (existingLockfileContents) {
+    // Read the pid number from the lockfile
+    const existingPid = Number(existingLockfileContents);
+
+    logger.debug("Lockfile exists", { lockFilePath, existingPid, currentPid });
+
+    if (existingPid === currentPid) {
+      logger.debug("Lockfile exists and is owned by current process", {
+        lockFilePath,
+        existingPid,
+        currentPid,
+      });
+
+      return () => {
+        removeExitListener();
+        removeLockFile();
+      };
+    }
+
+    // If the pid is different, try and kill the existing pid
+    logger.debug("Lockfile exists and is owned by another process, killing it", {
+      lockFilePath,
+      existingPid,
+      currentPid,
+    });
+
+    try {
+      process.kill(existingPid);
+      // If it did kill the process, it will have exited, deleting the lockfile, so let's wait for that to happen
+      // But let's not wait forever
+      await new Promise((resolve, reject) => {
+        const timeout = setTimeout(() => {
+          clearInterval(interval);
+          reject(new Error("Timed out waiting for lockfile to be deleted"));
+        }, 5000);
+
+        const interval = setInterval(() => {
+          if (!existsSync(lockFilePath)) {
+            clearInterval(interval);
+            clearTimeout(timeout);
+            resolve(true);
+          }
+        }, 100);
+      });
+    } catch (error) {
+      logger.debug("Failed to kill existing process, lets assume it's not running", { error });
+    }
+  }
+
+  // Now write the current pid to the lockfile
+  await writeFileAndEnsureDirExists(lockFilePath, currentPid.toString());
+
+  logger.debug("Lockfile created", { lockFilePath, currentPid });
+
+  return () => {
+    removeExitListener();
+    removeLockFile();
+  };
+}
+
+async function writeFileAndEnsureDirExists(filePath: string, data: string) {
+  const dir = path.dirname(filePath);
+  await mkdir(dir, { recursive: true });
+  await writeFile(filePath, data);
+}