trigger_device: The Glue That Wires Player Actions to Events

Overview

The trigger_device is a relay. Its whole job is to detect that something happened and then broadcast that fact so other things can react. The "something" is usually a player walking into its volume, but you can also fire it from Verse code with Trigger().

Reach for it whenever you want a player action to cause a consequence:

• Step on a pressure plate → open a vault door.
• Walk through a doorway → start a cinematic.
• Enter an arena → teleport every player into the action.

The device exposes one event you subscribe to — TriggeredEvent — and a handful of methods to drive it from code (Trigger), turn it on and off (Enable/Disable), and tune its behaviour (SetMaxTriggerCount, SetResetDelay, SetTransmitDelay). Because TriggeredEvent hands you the agent who triggered it, you can run player-specific logic — give that player a reward, teleport that character, and so on.

The key Verse rule to remember: you can't call methods on a placed device unless you declare it as an @editable field inside a class(creative_device), then point that field at the placed device in the UEFN Details panel.

API Reference

trigger_device

Used to relay events to other linked devices.

Full public surface, resolved verbatim from the live Epic digest (Fortnite.digest.verse). Inherited members are merged from trigger_base_device.

trigger_device<public> := class<concrete><final>(trigger_base_device):

Events (subscribe a handler to react):

Methods (call these to make the device act):

Walkthrough

Let's build a classic: a pressure plate that opens a vault door. We place a trigger_device on the floor where the player steps, and a second trigger_device wired (via Direct Event Binding in UEFN, or in code) to the door — but to keep everything in Verse and self-contained, we'll just react to the step directly and give the triggering player a celebratory message, then disable the plate so it only works once.

using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }
using { /UnrealEngine.com/Temporary/Diagnostics }
using { /Fortnite.com/Characters }

# Localized message helper — `message` params need a localizes value, not a raw string.
MyText<localizes>(S : string) : message = "{S}"

vault_room := class(creative_device):

    # The pressure plate the player steps on. Point this at the placed trigger in UEFN.
    @editable
    PressurePlate : trigger_device = trigger_device{}

    # A HUD message device to confirm the unlock (optional flavour).
    @editable
    UnlockMessage : hud_message_device = hud_message_device{}

    OnBegin<override>()<suspends> : void =
        # Only allow the plate to fire once, then stop reacting.
        PressurePlate.SetMaxTriggerCount(1)
        # Wait 0.5s after a trigger before the device tells other devices.
        PressurePlate.SetTransmitDelay(0.5)
        # Subscribe our handler to the event the plate fires when stepped on.
        PressurePlate.TriggeredEvent.Subscribe(OnPlateStepped)

    # TriggeredEvent hands us an OPTIONAL agent (?agent), because the device
    # can also be triggered from code with no agent attached.
    OnPlateStepped(MaybeAgent : ?agent) : void =
        if (Agent := MaybeAgent?):
            # We have a real player — confirm the vault is open just for them.
            UnlockMessage.Show(Agent)
            # Optional: react to their character (e.g. log position, etc.)
            if (Char := Agent.GetFortCharacter[]):
                Print("Player opened the vault!")
        # Whether or not there was an agent, lock the plate down so it won't refire.
        PressurePlate.Disable()

Line by line:

• MyText<localizes>(...) — a helper so we could pass a message; many message-taking APIs need localized text, never a raw string.
• @editable PressurePlate : trigger_device = trigger_device{} — declares the field. After compiling, you select your placed plate in the device's Details panel. Without this field you cannot call any method on the plate.
• OnBegin<override>()<suspends>:void = — runs when the device starts in a live game.
• SetMaxTriggerCount(1) — clamps the plate so it fires at most once.
• SetTransmitDelay(0.5) — delays the outgoing signal by half a second (useful if you later wire it to a door via the device's bindings).
• TriggeredEvent.Subscribe(OnPlateStepped) — registers our method as the reaction. Subscriptions happen in OnBegin.
• OnPlateStepped(MaybeAgent : ?agent) — the handler. The parameter is ?agent (optional!) because code-driven triggers send no agent.
• if (Agent := MaybeAgent?): — unwraps the option; the body only runs when a real player triggered it.
• UnlockMessage.Show(Agent) and Agent.GetFortCharacter[] — player-specific reactions.
• PressurePlate.Disable() — turns the device off so it stops reacting.

Common patterns

Fire a trigger from code to start a cinematic

You don't always wait for a player — sometimes your logic decides the moment. Here a different trigger is fired manually with Trigger(), which makes its own TriggeredEvent fire (with no agent). Wire that trigger to a cinematic in UEFN, and this code becomes your "play the cutscene now" button.

using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }

cinematic_starter := class(creative_device):

    # Plate the player walks through to enter the cutscene zone.
    @editable
    EntryPlate : trigger_device = trigger_device{}

    # This trigger is wired to a cinematic_sequence_device in UEFN bindings.
    @editable
    CinematicTrigger : trigger_device = trigger_device{}

    OnBegin<override>()<suspends> : void =
        EntryPlate.TriggeredEvent.Subscribe(OnEntered)

    OnEntered(MaybeAgent : ?agent) : void =
        if (Agent := MaybeAgent?):
            # Pass the agent along so the cinematic trigger knows who started it.
            CinematicTrigger.Trigger(Agent)
        else:
            # No agent (code path) — fire the agentless overload.
            CinematicTrigger.Trigger()

Reusable plate with a cooldown and a budget

Use SetResetDelay for a cooldown between activations and SetMaxTriggerCount for a total budget. You can read the remaining budget with GetTriggerCountRemaining to react when the supply runs out.

using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }
using { /UnrealEngine.com/Temporary/Diagnostics }

loot_dispenser := class(creative_device):

    @editable
    LootPlate : trigger_device = trigger_device{}

    OnBegin<override>()<suspends> : void =
        # Can be used 5 times total, with a 3-second cooldown between uses.
        LootPlate.SetMaxTriggerCount(5)
        LootPlate.SetResetDelay(3.0)
        LootPlate.TriggeredEvent.Subscribe(OnLootGrabbed)

    OnLootGrabbed(MaybeAgent : ?agent) : void =
        Remaining := LootPlate.GetTriggerCountRemaining()
        Print("Loot grabbed. Charges left: {Remaining}")
        if (Remaining = 0):
            # Budget exhausted — shut the dispenser down.
            LootPlate.Disable()

Read configured delays back out

The getters let your logic stay in sync with whatever you set in the Details panel or in code. Here we mirror the plate's reset delay into a Sleep so a follow-up effect lines up perfectly.

using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }
using { /UnrealEngine.com/Temporary/Diagnostics }

synced_plate := class(creative_device):

    @editable
    Plate : trigger_device = trigger_device{}

    OnBegin<override>()<suspends> : void =
        Plate.SetResetDelay(2.0)
        Plate.TriggeredEvent.Subscribe(OnStepped)

    OnStepped(MaybeAgent : ?agent) : void =
        spawn{ WaitForReset() }

    WaitForReset()<suspends> : void =
        Delay := Plate.GetResetDelay()
        Sleep(Delay)
        Print("Plate is ready again after {Delay} seconds.")

Gotchas

• TriggeredEvent sends ?agent, not agent. The device can be fired from code with no player, so the payload is optional. Always unwrap with if (Agent := MaybeAgent?): before using it. Trying to call Agent.GetFortCharacter[] on the raw ?agent won't compile.
• You must have the @editable field, AND bind it in UEFN. A bare trigger_device{} field that you never point at a placed device will silently do nothing — Enable, Trigger, etc. operate on an unset device.
• SetMaxTriggerCount is clamped to [0,20]. Passing 0 means unlimited, not zero — and GetTriggerCountRemaining() returns 0 when the max is unlimited, so don't treat a 0 remaining as "empty" if you set the max to 0.
• Trigger() vs Trigger(Agent). The agentless overload makes TriggeredEvent fire with false/no agent; subscribers' ?agent will be empty. Use Trigger(Agent) when downstream logic needs to know who.
• Subscribe in OnBegin, not in a constructor. Event subscriptions must happen at runtime. Calling .Subscribe outside the running device's lifecycle won't hook anything up.
• message params need localized text. If you call a method that takes a message, use a <localizes> helper like MyText("..."). There is no StringToMessage.
• Verse never auto-converts int↔float. SetResetDelay takes a float (2.0), SetMaxTriggerCount takes an int (5). Mixing them up is a compile error.