diff --git a/src/omni_pca/program_engine.py b/src/omni_pca/program_engine.py
index 783a39a..bc92ed6 100644
--- a/src/omni_pca/program_engine.py
+++ b/src/omni_pca/program_engine.py
@@ -418,6 +418,64 @@ def _command_payload(program: Program) -> bytes:
     )
 
 
+# --------------------------------------------------------------------------
+# Event taxonomy
+# --------------------------------------------------------------------------
+
+
+# Event-ID encoding mirrors clsText.GetEventCategory (clsText.cs:1585-...).
+# Each event has a 16-bit ID; bit-pattern masks pick out the category, and
+# the low-order bits within each category encode the object number / state.
+# We expose helper builders rather than a full enuEventType mirror — the
+# common cases below cover what TIMED-program authors actually wire up.
+
+
+def event_id_user_macro_button(button: int) -> int:
+    """Event ID fired when a panel button macro runs.
+
+    Category mask: ``(evt & 0xFF00) == 0x0000``. The low byte holds the
+    1-based button number (1..255).
+    """
+    if not 1 <= button <= 255:
+        raise ValueError(f"button {button} out of range 1..255")
+    return button & 0xFF
+
+
+def event_id_zone_state(zone: int, state: int) -> int:
+    """Event ID for a zone-state change.
+
+    Category mask: ``(evt & 0xFC00) == 0x0400`` (high bits 0b000001).
+    Low 10 bits encode zone × state per clsText: ``(zone - 1) * 4 + state``
+    where state is the 2-bit "current_state" code (0=secure, 1=not-ready,
+    2=trouble, 3=tamper). Range fits 256 zones × 4 states = 1024 IDs.
+    """
+    if not 1 <= zone <= 256:
+        raise ValueError(f"zone {zone} out of range 1..256")
+    if not 0 <= state <= 3:
+        raise ValueError(f"state {state} out of range 0..3")
+    return 0x0400 | (((zone - 1) * 4 + state) & 0x03FF)
+
+
+def event_id_unit_state(unit: int, on: bool) -> int:
+    """Event ID for a unit (light/output) state change.
+
+    Category mask: ``(evt & 0xFC00) == 0x0800``. Low bits encode
+    ``(unit - 1) * 2 + (1 if on else 0)`` per clsText.
+    """
+    if not 1 <= unit <= 511:
+        raise ValueError(f"unit {unit} out of range 1..511")
+    return 0x0800 | (((unit - 1) * 2 + (1 if on else 0)) & 0x03FF)
+
+
+# Hand-rolled fixed-ID events from clsText.cs:1647-... (PHONE/AC_POWER/etc.).
+EVENT_PHONE_DEAD: int = 768
+EVENT_PHONE_RINGING: int = 769
+EVENT_PHONE_OFF_HOOK: int = 770
+EVENT_PHONE_ON_HOOK: int = 771
+EVENT_AC_POWER_OFF: int = 772
+EVENT_AC_POWER_ON: int = 773
+
+
 # --------------------------------------------------------------------------
 # Engine
 # --------------------------------------------------------------------------
@@ -478,6 +536,10 @@ class ProgramEngine:
         self._classified = classify(self._programs)
         self._tasks: list[asyncio.Task[None]] = []
         self._running = False
+        # event_id → list of EVENT programs that fire on it. Built lazily
+        # in start() so callers can mutate state.programs between init
+        # and start (e.g. a test seeding extra programs).
+        self._event_table: dict[int, list[Program]] = {}
         self.metrics = _EngineMetrics()
 
     # ---- inspection -------------------------------------------------------
@@ -523,6 +585,12 @@ class ProgramEngine:
                     name=f"omni-pca-yearly-slot-{program.slot}",
                 )
             )
+        # Phase 4: EVENT programs aren't long-running tasks — they just
+        # register in the event table and the engine dispatches on
+        # emit_event(). Build the table now so emit is O(1).
+        self._event_table.clear()
+        for program in self._classified.event:
+            self._event_table.setdefault(program.event_id, []).append(program)
 
     async def _run_timed_program(self, program: Program) -> None:
         """Sleep-until-next-fire loop for one TIMED program.
@@ -560,6 +628,43 @@ class ProgramEngine:
             )
             self.metrics.errors += 1
 
+    # ---- event dispatch (Phase 4) ----------------------------------------
+
+    async def emit_event(self, event_id: int) -> int:
+        """Fire every EVENT program subscribed to ``event_id``.
+
+        Returns the number of programs that fired. Safe to call before
+        ``start()`` (returns 0 since no event table is built yet) or
+        after ``stop()`` (programs registered while running aren't
+        retained — call start again to rebuild).
+
+        The classic use cases are wired up via the convenience helpers
+        below, but tests and HA code can also call this directly with
+        any raw ``event_id``.
+        """
+        if not self._running:
+            return 0
+        programs = self._event_table.get(event_id, ())
+        for program in programs:
+            await self._fire(program)
+        return len(programs)
+
+    async def emit_user_macro_button(self, button: int) -> int:
+        """Convenience: fire EVENT programs subscribed to a button press."""
+        return await self.emit_event(event_id_user_macro_button(button))
+
+    async def emit_zone_state(self, zone: int, state: int) -> int:
+        """Convenience: fire EVENT programs subscribed to a zone-state change.
+
+        ``state`` is the 2-bit current_state code: 0=secure, 1=not-ready,
+        2=trouble, 3=tamper. Matches MockZoneState.current_state.
+        """
+        return await self.emit_event(event_id_zone_state(zone, state))
+
+    async def emit_unit_state(self, unit: int, on: bool) -> int:
+        """Convenience: fire EVENT programs subscribed to a unit on/off."""
+        return await self.emit_event(event_id_unit_state(unit, on))
+
     async def _run_yearly_program(self, program: Program) -> None:
         """Sleep-until-next-fire loop for one YEARLY program."""
         try:
diff --git a/tests/test_program_engine.py b/tests/test_program_engine.py
index 6e2f5dc..0f53a47 100644
--- a/tests/test_program_engine.py
+++ b/tests/test_program_engine.py
@@ -601,6 +601,152 @@ async def test_engine_sun_relative_without_location_is_skipped() -> None:
         assert engine.metrics.timed_fired == 0
 
 
+# ---- Phase 4: EVENT programs --------------------------------------------
+
+
+from omni_pca.program_engine import (  # noqa: E402
+    EVENT_AC_POWER_OFF,
+    event_id_unit_state,
+    event_id_user_macro_button,
+    event_id_zone_state,
+)
+
+
+def test_event_id_user_macro_button_packs_low_byte() -> None:
+    assert event_id_user_macro_button(1) == 0x0001
+    assert event_id_user_macro_button(255) == 0x00FF
+
+
+def test_event_id_user_macro_button_rejects_out_of_range() -> None:
+    with pytest.raises(ValueError):
+        event_id_user_macro_button(0)
+    with pytest.raises(ValueError):
+        event_id_user_macro_button(256)
+
+
+def test_event_id_zone_state_encodes_zone_and_state() -> None:
+    # Zone 1 state 0 (secure) → 0x0400 base.
+    assert event_id_zone_state(1, 0) == 0x0400
+    assert event_id_zone_state(1, 3) == 0x0403  # tamper
+    # Zone 2 state 0 = 0x0404 (2-1)*4+0
+    assert event_id_zone_state(2, 0) == 0x0404
+
+
+def test_event_id_unit_state_encodes_unit_and_on_off() -> None:
+    assert event_id_unit_state(1, on=False) == 0x0800
+    assert event_id_unit_state(1, on=True) == 0x0801
+    assert event_id_unit_state(2, on=True) == 0x0803
+
+
+@pytest.mark.asyncio
+async def test_engine_emit_event_fires_subscribed_program() -> None:
+    """An EVENT program with event_id matching the emit fires."""
+    button_evt = event_id_user_macro_button(5)
+    # EVENT program stores event_id in (month<<8)|day per programs.event_id.
+    p = Program(
+        slot=1, prog_type=int(ProgramType.EVENT),
+        cmd=int(Command.UNIT_ON), pr2=7,
+        month=(button_evt >> 8) & 0xFF, day=button_evt & 0xFF,
+    )
+    panel = _panel_with_programs(p)
+    async with ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    )) as engine:
+        fired = await engine.emit_user_macro_button(5)
+        assert fired == 1
+        assert engine.metrics.event_fired == 1
+        assert panel.state.units[7].state == 1
+
+
+@pytest.mark.asyncio
+async def test_engine_emit_event_no_match_returns_zero() -> None:
+    """Emitting an event with no subscribed program is a silent no-op."""
+    panel = MockPanel(controller_key=CONTROLLER_KEY, state=MockState())
+    async with ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    )) as engine:
+        assert await engine.emit_user_macro_button(99) == 0
+        assert engine.metrics.event_fired == 0
+
+
+@pytest.mark.asyncio
+async def test_engine_emit_event_before_start_is_no_op() -> None:
+    """emit_event on an un-started engine doesn't raise — just returns 0."""
+    p = Program(
+        slot=1, prog_type=int(ProgramType.EVENT),
+        cmd=1, month=0, day=1,
+    )
+    panel = _panel_with_programs(p)
+    engine = ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    ))
+    assert await engine.emit_event(1) == 0  # not started yet
+
+
+@pytest.mark.asyncio
+async def test_engine_multiple_programs_on_same_event() -> None:
+    """Two EVENT programs subscribed to the same event both fire."""
+    evt = event_id_user_macro_button(3)
+    hi = (evt >> 8) & 0xFF
+    lo = evt & 0xFF
+    p1 = Program(
+        slot=1, prog_type=int(ProgramType.EVENT),
+        cmd=int(Command.UNIT_ON), pr2=5,
+        month=hi, day=lo,
+    )
+    p2 = Program(
+        slot=2, prog_type=int(ProgramType.EVENT),
+        cmd=int(Command.UNIT_ON), pr2=6,
+        month=hi, day=lo,
+    )
+    panel = _panel_with_programs(p1, p2)
+    async with ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    )) as engine:
+        fired = await engine.emit_user_macro_button(3)
+        assert fired == 2
+        assert panel.state.units[5].state == 1
+        assert panel.state.units[6].state == 1
+
+
+@pytest.mark.asyncio
+async def test_engine_zone_state_emit_helper() -> None:
+    """emit_zone_state fires programs matching that exact (zone, state)."""
+    evt = event_id_zone_state(7, 1)  # zone 7 not-ready
+    p = Program(
+        slot=10, prog_type=int(ProgramType.EVENT),
+        cmd=int(Command.UNIT_ON), pr2=12,
+        month=(evt >> 8) & 0xFF, day=evt & 0xFF,
+    )
+    panel = _panel_with_programs(p)
+    async with ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    )) as engine:
+        # Wrong state — no fire.
+        assert await engine.emit_zone_state(7, 0) == 0
+        assert engine.metrics.event_fired == 0
+        # Right state — fire.
+        assert await engine.emit_zone_state(7, 1) == 1
+        assert engine.metrics.event_fired == 1
+
+
+@pytest.mark.asyncio
+async def test_engine_fixed_event_constants() -> None:
+    """The hand-rolled fixed-ID events (PHONE/AC_POWER) dispatch correctly."""
+    p = Program(
+        slot=1, prog_type=int(ProgramType.EVENT),
+        cmd=int(Command.UNIT_ON), pr2=4,
+        month=(EVENT_AC_POWER_OFF >> 8) & 0xFF,
+        day=EVENT_AC_POWER_OFF & 0xFF,
+    )
+    panel = _panel_with_programs(p)
+    async with ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    )) as engine:
+        fired = await engine.emit_event(EVENT_AC_POWER_OFF)
+        assert fired == 1
+
+
 @pytest.mark.asyncio
 async def test_engine_fires_sun_relative_program_with_location() -> None:
     """End-to-end: TIMED AT_SUNSET program fires at astral-computed