diff --git a/demo/apps/myapp/mystatemachine.go b/demo/apps/myapp/mystatemachine.go
new file mode 100644
index 0000000..1c3d322
--- /dev/null
+++ b/demo/apps/myapp/mystatemachine.go
@@ -0,0 +1,121 @@
+package myapp
+
+import (
+	"time"
+
+	"ergo.services/ergo/act"
+	"ergo.services/ergo/gen"
+)
+
+// Code Lock, inspired by https://www.erlang.org/doc/system/statem.html#example-revisited
+
+type CodeLockData struct {
+	buttons []int
+	code    [4]int
+}
+
+type CodeLock struct {
+	act.StateMachine[CodeLockData]
+}
+
+func factoryCodeLock() gen.ProcessBehavior {
+	return &CodeLock{}
+}
+
+type ButtonPress struct {
+	Button int
+}
+
+type Lock struct{}
+
+type ResetCode struct{}
+
+type CodeLength struct{}
+
+func (order *CodeLock) Init(args ...any) (act.StateMachineSpec[CodeLockData], error) {
+	spec := act.NewStateMachineSpec(
+		// The initial state.
+		gen.Atom("locked"),
+
+		// The initial data.
+		act.WithData(CodeLockData{}),
+
+		// Register a function that is called on every state change.
+		act.WithStateEnterCallback(enterState),
+
+		// Register a handler for the ButtonPress message
+		act.WithStateMessageHandler(gen.Atom("open"), handleButtonPress),
+
+		// Register the handler for the Lock message.
+		act.WithStateMessageHandler(gen.Atom("open"), handleLock),
+
+		// Register the handler for the ResetCode message.
+		act.WithStateMessageHandler(gen.Atom("open"), handleResetCode),
+
+		// Register handler for retrieving the length of the code (it would
+		// be nice to have an all-state handler for this)
+		act.WithStateCallHandler(gen.Atom("open"), handleCodeLength),
+		act.WithStateCallHandler(gen.Atom("locked"), handleCodeLength),
+	)
+
+	return spec, nil
+}
+
+func enterState(oldState gen.Atom, newState gen.Atom, data CodeLockData, proc gen.Process) (gen.Atom, CodeLockData, error) {
+	proc.Log().Info("state changed to %s", newState)
+	return newState, data, nil
+}
+
+func handleButtonPress(state gen.Atom, data CodeLockData, msg ButtonPress, proc gen.Process) (gen.Atom, CodeLockData, []act.Action, error) {
+	data.buttons = append(data.buttons, msg.Button)
+	if len(data.buttons) < len(data.code) {
+		// code incomplete
+		// reset code after 30 seconds of inactivity
+		reset := act.MessageTimeout{
+			Duration: 30 * time.Second,
+			Message:  ResetCode{},
+		}
+		return state, data, []act.Action{reset}, nil
+	}
+	for i, b := range data.buttons {
+		if b != data.code[i] {
+			// incorrect code
+			// reset buttons
+			data.buttons = nil
+			return state, data, nil, nil
+		}
+	}
+	// code is correct
+	// reset buttons
+	// automatically lock after 10 seconds
+	data.buttons = nil
+	lockAfter10Seconds := act.StateTimeout{
+		Duration: 10 * time.Second,
+		Message:  Lock{},
+	}
+	return gen.Atom("open"), data, []act.Action{lockAfter10Seconds}, nil
+}
+
+func handleLock(state gen.Atom, data CodeLockData, msg Lock, proc gen.Process) (gen.Atom, CodeLockData, []act.Action, error) {
+	doLock()
+	data.buttons = nil
+	return gen.Atom("locked"), data, nil, nil
+}
+
+func handleResetCode(state gen.Atom, data CodeLockData, msg ResetCode, proc gen.Process) (gen.Atom, CodeLockData, []act.Action, error) {
+	data.buttons = nil
+	return state, data, nil, nil
+}
+
+func handleCodeLength(state gen.Atom, data CodeLockData, msg Lock, proc gen.Process) (gen.Atom, CodeLockData, int, []act.Action, error) {
+	doLock()
+	return state, data, len(data.code), nil, nil
+}
+
+func doLock() {
+	// interact with the hardware
+}
+
+func doUnlock() {
+	// interact with the hardware
+}
diff --git a/demo/go.mod b/demo/go.mod
index f3904b4..3347dce 100644
--- a/demo/go.mod
+++ b/demo/go.mod
@@ -3,16 +3,17 @@ module demo
 go 1.21.6
 
 require (
-	ergo.services/application v0.0.0-20240904055159-7f2e1a954c05
-	ergo.services/ergo v1.999.300
-	ergo.services/logger v0.0.0-20240904054830-18407beea628
-)
+        ergo.services/application v0.0.0-20240904055159-7f2e1a954c05
+        ergo.services/ergo v1.999.300
+        ergo.services/logger v0.0.0-20240904054830-18407beea628
+        )
 
 require (
-	ergo.services/meta v0.0.0-20240904054930-a97f6add8a78 // indirect
-	github.com/fatih/color v1.16.0 // indirect
-	github.com/gorilla/websocket v1.5.0 // indirect
-	github.com/mattn/go-colorable v0.1.13 // indirect
-	github.com/mattn/go-isatty v0.0.20 // indirect
-	golang.org/x/sys v0.14.0 // indirect
-)
+        ergo.services/meta v0.0.0-20240904054930-a97f6add8a78 // indirect
+        github.com/fatih/color v1.16.0 // indirect
+        github.com/gorilla/websocket v1.5.0 // indirect
+        github.com/mattn/go-colorable v0.1.13 // indirect
+        github.com/mattn/go-isatty v0.0.20 // indirect
+        golang.org/x/sys v0.14.0 // indirect
+        )
+