Sound sensitive trigger

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This tutorial will explain the process of making a trigger that will detect sound levels in the surrounding area and go off.

Soundsensitive first.jpg

Getting started

First of all, you need a small area for this example. The area for this tutorial is a small courtyard, as shown on the right.

Setting up the necessary entities

We need something for the microphone to detect from. An info_target is what we will be using. Call it microphone1. In your map, it can be called anything you like.

Soundsensitive second.jpg

Then, create an env_microphone. This is the entity that will control the sound output level. Give it the following properties:

Classname : env_microphone

  • Name : speaker In your map again, this can be anything at all.
  • Measure Target : microphone1 Make sure this is the name of your info_target, otherwise the env_microphone won't do its sound checks correctly.
  • Sensitivity : 2 This should allow you to not be detected by crouching, but will detect you when you run or shoot.
  • Maximum hearing range : 512 This is the distance in units the env_microphone will hear.
  • Spawnflags :
  • Hears combat sounds
  • Hears world sounds
  • Hears player sounds
  • Hears bullet impacts
  • Hears explosions

Now we need a logic_compare to test the sound levels. We need the following parameters for it:

Classname : logic_compare

  • Name : spvol Our entity's name again, this entity checks the volume of the microphone and can trigger things.
  • Initial value : 0 This is what the logic_compare will compare all values to, and can trigger an output depending on various states.
  • Compare value : 0.5 This is the trigger level to trigger things from the sound level of the env_microphone.

Now we need to set up some of the entity I/O on our env_microphone. Add a new output to our env_microphone with the following options:

Object outputs: speaker - env_microphone
My Output Target Entity Target Input Parameter Delay Only Once
Io11.png SoundLevel spvol SetValueCompare <none> 0.00 No
Soundsensitive third.jpg

Making the trigger

The final step now is to set up the output of the logic_compare to trigger something. This can be open a door, turn on a light, break a rope, anything that can take an entity I/O input. In this case we will rig up an alarm.


  • OnGreaterThan: This gets triggered when the sound level is past the trigger level.
  • OnLessThan: This gets triggered when the sound level is under the trigger level.

Now you should have a working sound sensitive trigger!

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