# llVolumeDetect

*LSL function*

```lsl
void llVolumeDetect(integer detect);
```

- `integer detect`: Boolean. If TRUE, enables VolumeDetect; if FALSE (default), disables it.

- Energy: 10

If **detect** is [TRUE](/constants/TRUE/), VolumeDetect is enabled, physical object and avatars can pass through the object.

This works much like Phantom, but unlike Phantom, VolumeDetect objects trigger [collision_start](/events/collision_start/) and [collision_end](/events/collision_end/) events when interpenetrating. Collision events will trigger in any script in the object.

```lsl title="How to use" frame="terminal"
llVolumeDetect(0);
```

## Specification

**Events queued depending on type**

|  | VolumeDetect | Phantom |
| --- | --- | --- |
| Events<br />Supported | [collision_start](/events/collision_start/)<br /><br />[collision_end](/events/collision_end/) | [land_collision_start](/events/land_collision_start/)<br />[land_collision](/events/land_collision/)<br />[land_collision_end](/events/land_collision_end/) |

#### Differences

There are a couple differences in how Phantom and VolumeDetect handle collisions; specifically which events are supported and how they handle the ground.

###### VolumeDetect

- When physical they fall through the ground with the risk of going off-world.
- [collision](/events/collision/) events are not triggered

###### Phantom

- When physical they collide with the ground but will not pass through (normal physical object behavior), [land collision](https://wiki.secondlife.com/wiki/Category:LSL_Land_Collision) events are queued.

## Caveats

- It can only be applied to the root prim (which will make the entire object VolumeDetect).
- If the volume detecting object is *not* physical, it can only detect physical objects and avatars. If the object *is* physical, it can detect its collisions with static and [keyframed motion](/functions/llSetKeyframedMotion/) objects as well.

### Attachments

**Note:** Attachments are not included in the avatar's bounding box. [Collision events](https://wiki.secondlife.com/wiki/Category:LSL_Collision) received by attachments are collisions the avatar is having with the world, not collisions the attachment is having. Nothing actually can collide with an attachment[^wiki-f918c3].

- It is meaningless to enabled on attachments. Attachments cannot collide with anything.
- Attachments do not receive collision events for avatar collisions with VolumeDetect objects.
  - Attachments do receive collision events for avatar collisions with non-VolumeDetect, non-phantom objects.

[^wiki-f918c3]: Even if attachments were included in an avatars bounding box, you would not like the outcome, the avatars bounding box is not deformed by animations.

## Examples

<details open>
<summary>Example 1</summary>

```lsl
default
{
    state_entry()
    {
        llVolumeDetect(TRUE); // Starts llVolumeDetect
    }
    collision_start(integer total_number)
    {
        llSay(0, "Detected!"); // Tells you when something penetrates the prim
    }
}
```

</details>

## Known issues

From the issue templates included by the wiki article:

- SVC-2490 (bug): llCollisionFilter completely ignored after call to user-defined function and then a call to llVolumeDetect(TRUE)
- SVC-8141 (bug): Volume Detect objects are not always allowing objects to pass through.
- SVC-2996 (fs): llDetectedLinkNumber returns 0 with llVolumeDetect(TRUE)

## See also

### Functions

- [llPassCollisions](/functions/llPassCollisions/)

### Events

- [collision_start](/events/collision_start/)
- [collision](/events/collision/)
- [collision_end](/events/collision_end/)

---

*Source: [LlVolumeDetect](https://wiki.secondlife.com/wiki/LlVolumeDetect) on the Second Life Wiki. Content from the Second Life Wiki articles LlVolumeDetect (revision 1217514, 2024-10-11), Template:Issues/SVC-2490 (revision 1186584, 2014-01-07), Template:Issues/SVC-8141 (revision 1172031, 2012-08-23), Template:Issues/SVC-2996 (revision 1179320, 2013-06-19) and Template:LSL Function/boolean (revision 1185613, 2013-12-24), CC BY-SA 3.0.*

---

From lsl.dev: https://lsl.dev/functions/llVolumeDetect/