diff --git a/sbot/robot.py b/sbot/robot.py
index f002ede..22e8ec6 100644
--- a/sbot/robot.py
+++ b/sbot/robot.py
@@ -55,17 +55,18 @@ def __init__(
         trace_logging: bool = False,
         manual_boards: dict[str, list[str]] | None = None,
     ) -> None:
-        self._lock = obtain_lock()
+        if IN_SIMULATOR:
+            self._lock = TimeServer.initialise()
+            if self._lock is None:
+                raise OSError('Unable to obtain lock, Is another robot instance already running?')
+        else:
+            self._lock = obtain_lock()
         self._metadata: Metadata | None = None
 
         setup_logging(debug, trace_logging)
         ensure_atexit_on_term()
 
         logger.info(f"SourceBots API v{__version__}")
-        if IN_SIMULATOR:
-            self._time_server = TimeServer.initialise()
-        else:
-            self._time_server = None
 
         if manual_boards:
             self._init_power_board(manual_boards.get(PowerBoard.get_board_type(), []))
@@ -255,7 +256,8 @@ def sleep(self, secs: float) -> None:
         :param secs: The number of seconds to sleep for
         """
         if IN_SIMULATOR:
-            self._time_server.sleep(secs)
+            assert isinstance(self._lock, TimeServer)
+            self._lock.sleep(secs)
         else:
             sleep(secs)