How to play a sound fx by script? AudioGizmo does not show in Gizmos? Only Sound Recorder

You can play a sound gizmo in TypeScript like this:

this.entity.as(AudioGizmo).play();

That line tells the entity to cast itself as an AudioGizmo and then run the play() method.

If you want a step-by-step walkthrough, i broke it down in this video:  https://youtu.be/nFMWiJHWPnY

Here is another common use case: 
You attach this script to a trigger gizmo in your scene and drag your audioGizmo from the Hierarchy into the AudioSource slot in the Properties panel. 
When the player enters the trigger, the SFX plays.

You can also use a cooldown to prevent the audio from triggering too frequently. The cooldown is 2000 milliseconds by default. 

import * as hz from "horizon/core";

class AudioOnTrigger extends hz.Component<typeof AudioOnTrigger> {
  static propsDefinition = {
    // Assign an entity that has an Audio gizmo
    audioSource: { type: hz.PropTypes.Entity },
    // Optional: prevent rapid re-triggers (ms)
    cooldownMs: { type: hz.PropTypes.Number, default: 2000 },
  };

  private lastTriggerTime = 0;

  start(): void {
    this.connectCodeBlockEvent(
      this.entity,
      hz.CodeBlockEvents.OnPlayerEnterTrigger,
      (_player: hz.Player) => {
        const now = Date.now();
        if (now - this.lastTriggerTime < (this.props.cooldownMs ?? 0)) return; // cooldown
        this.lastTriggerTime = now;

        const src = this.props.audioSource;
        if (!src) { console.warn("[AudioOnTrigger] Assign audioSource."); return; }

        const audio = src.as(hz.AudioGizmo);
        if (!audio) { console.warn("[AudioOnTrigger] audioSource has no Audio gizmo."); return; }

        try { audio.play(); } catch (e) { console.warn("[AudioOnTrigger] play failed:", e); }
      }
    );
  }
}

hz.Component.register(AudioOnTrigger);