# llCollisionFilter

*LSL function*

```lsl
void llCollisionFilter(string name, key id, integer accept);
```

- `string name`: Specific object name or avatar legacy name to filter for.
- `key id`: Group, avatar, or object UUID to filter by.
- `integer accept`: Boolean. If TRUE, only collisions matching the name and id filters are processed; if FALSE, matching collisions are excluded.

- Energy: 10

Sets the collision filter, exclusively or inclusively.

If **accept** == [TRUE](/constants/TRUE/), only accept collisions with objects **name** AND **id** (either is optional), otherwise with objects not **name** AND **id**

If **name** or **id** are blank they are not used to filter incoming messages (or you could say they match everything).

If **id** is an invalid key or a [null key](/constants/NULL_KEY/), it is considered blank.

```lsl title="How to use" frame="terminal"
llCollisionFilter("", NULL_KEY, 0);
```

## Caveats

- Any call of `llCollisionFilter` in the same event as [llVolumeDetect](/functions/llVolumeDetect/) changing (not just being called, but actually moving from [FALSE](/constants/FALSE/) to [TRUE](/constants/TRUE/) or vice versa) will be disregarded (before or after), **if** the event handler previously called a user-defined function. See [svc 2490](#svc-2490)
- You can get around this by calling them in separate events, such as [touch_start](/events/touch_start/) and [touch_end](/events/touch_end/).
- Damage caused by [llSetDamage](/functions/llSetDamage/) will still apply to a filtered avatar.
- Consequently, the object will immediately die on collision with the avatar. (And kill the avatar their health reaches 0.)

## Examples

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

- Stop filtering:

```lsl
llCollisionFilter("", NULL_KEY, TRUE);
```

</details>

<details>
<summary>Example 2</summary>

- Filter out all collisions:

```lsl
llCollisionFilter("", NULL_KEY, FALSE);
```

</details>

<details>
<summary>This script, placed in a wearable object, detects a collision when the person wearing it collides with an object named "Post":</summary>

- 1st instance :

an object named "Post" has several child prims named "Object" .

The prim named "Post" hits the scripted object or scripted prim , the collision will be detected

- 2nd instance :

an object named "Post" has several child prims named "Object" .

A child prim named "Object" hits the scripted object or scripted prim, the collision will be detected

- 3rd instance :

an object named "Object" has several child prims named "Post" .

A prim named "Post" hits the scripted object or scripted prim, the collision will not be detected

```lsl
default
{
    state_entry()
    {
        llCollisionFilter("Post","",TRUE);
    }

    collision_start(integer total_number)
    {
        llSay(0, "OUCH!");
    }
}
```

</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)

## See also

### Functions

- [llPassCollisions](/functions/llPassCollisions/)
- [llVolumeDetect](/functions/llVolumeDetect/)

### Events

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

---

*Source: [LlCollisionFilter](https://wiki.secondlife.com/wiki/LlCollisionFilter) on the Second Life Wiki. Content from the Second Life Wiki articles LlCollisionFilter (revision 1218612, 2026-02-03), Template:Issues/SVC-2490 (revision 1186584, 2014-01-07), Template:LSL Function/uuid (revision 1195911, 2015-03-21) and Template:LSL Function/boolean (revision 1185613, 2013-12-24), CC BY-SA 3.0.*

---

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