diff --git a/tests/unit/test_pin_unification.py b/tests/unit/test_pin_unification.py
new file mode 100644
index 0000000..9864445
--- /dev/null
+++ b/tests/unit/test_pin_unification.py
@@ -0,0 +1,45 @@
+"""End-to-end test: the CLI, FSM, and web arm flow all accept the same PIN.
+
+Regression guard for issue #2 — the three layers previously used three
+incompatible hash schemes under two different config keys."""
+
+from click.testing import CliRunner
+
+from vigilar.alerts.pin import hash_pin, verify_pin
+from vigilar.cli.cmd_config import config_cmd
+from vigilar.config import SecurityConfig, VigilarConfig
+from vigilar.events.state import ArmStateFSM
+from vigilar.constants import ArmState
+
+
+def test_cli_output_is_accepted_by_fsm(test_db):
+    """Hash produced by `vigilar config set-pin` must verify against
+    ArmStateFSM.verify_pin, same config key, same format."""
+    runner = CliRunner()
+    result = runner.invoke(config_cmd, ["set-pin"], input="9876\n9876\n")
+    assert result.exit_code == 0, result.output
+
+    hash_line = next(
+        line for line in result.output.splitlines()
+        if line.strip().startswith("pin_hash")
+    )
+    hash_value = hash_line.split('"')[1]
+
+    cfg = VigilarConfig(security=SecurityConfig(pin_hash=hash_value))
+    fsm = ArmStateFSM(test_db, cfg)
+
+    assert fsm.verify_pin("9876") is True
+    assert fsm.verify_pin("0000") is False
+
+
+def test_fsm_transitions_with_pin_from_alerts_module(test_db):
+    """The alerts.pin module and ArmStateFSM agree on the hash format."""
+    stored = hash_pin("4242")
+    cfg = VigilarConfig(security=SecurityConfig(pin_hash=stored))
+    fsm = ArmStateFSM(test_db, cfg)
+
+    assert fsm.transition(ArmState.ARMED_AWAY, pin="4242", triggered_by="test") is True
+    assert fsm.state == ArmState.ARMED_AWAY
+
+    # Same stored hash rejects the wrong PIN
+    assert verify_pin("0000", stored) is False