on touch is an AV within 3 meters

I want to know if an specific avatar (by key) is within a set distance (x.y.z) of a prim when the prim is touched - any ideas?

llVecDist(llGetPos(),llDetectedPos(0)); will give you the distance when they touch.
You will have to do an llDetectedKey(0) test to see if it is the desired avatar.

I answered my own question:

float range = 3.0; // metres
key reader_key;
key reader_name_query;
integer online = FALSE;
string whotocheck= "";

default
{
//====== Gather info ======
touch(integer touch_num)
{
reader_key = (key)llGetObjectDesc ();
//Who is the current reader
whotocheck = llDetectedKey(0);
//Who wants to read

//====== Check if 'Whoto check' is the curret reader ======

if(reader_key != whotocheck)
//check if current reader and new reader are the same person
{
llSay(0,"You are not the current reader reader.";//Test value
//====== Check if current reader is offline ======
llRequestAgentData(reader_key, DATA_ONLINE);
}
}
dataserver(key queryid, string data)//Get the result of the request
{
llSay(0,data); //Test value
if (data == "1"// If reader is online
//====== Check if reader is within 3 meters ======
{
llSensor("", reader_key, AGENT, range, PI); //see float range varaible)
}
}
sensor (integer numberDetected)//Get scan result
{
string msg = "Detected " + llDetectedName(0);//turn result into a string
integer i = 0;//Garbbage collection
{
msg += ", " + llDetectedName(i);//cleaning out the string
}
llSay(0, msg);//Test value
llSetText("Go to Bookmark", <0,1,0>, 1);
}

no_sensor()//If not within 3 meters
{
llSay(0, "Previous reader is not near me.";//Test value
llSetText("Closed Book", <0,1,0>, 1);
}
}

Thanks AnnMarie - I didn't see your reply before I posted my code - I'll check your suggestion out

llGetObjectDetails() is your friend...

// key Avatar;
// float Limit;
//
//
vector pos = llList2Vector(llGetObjectDetails(Avatar, [OBJECT_POS]), 0);
if (pos != ZERO_VECTOR) // Avatar in sim
{
if (llVecDist(llGetPos(), pos) < Limit) // Within limit
{
llSay(0, "Gotcha!";
}
}

There was a reply by Kaluura ?? but it dropped off before I got to read it!

Sorry... There was a burst of answers when I finished so I just deleted mine. I'm re-posting because I was proposing a lag free alternative to a server request plus a sensor.

I honestly don't understand what you're trying to do with that script so I just imitated the behavior of yours...

float range = 3.0; // metres
key reader_key;

default
{
touch_start(integer touch_num)
{
reader_key = (key)llGetObjectDesc ();
if (reader_key != llDetectedKey(0))
{
llSay(0,"You are not the current reader.";
vector pos = llList2Vector(llGetObjectDetails(reader_key, [OBJECT_POS]), 0);
if ( (pos != ZERO_VECTOR) // In the sim
&& (llVecDist(llGetPos(), pos) < range) ) // Within range
{
string msg = "Detected " + llKey2Name(reader_key);
integer i = llGetRegionAgentCount() - 1;
if (i)
{
msg += " and " + llList2String(["another avatar", (string)i + " avatars"], (i > 1)) + " in the region";
}
llSay(0, msg);//Test value
llSetText("Go to Bookmark", <0,1,0>, 1);
}
else
{
// Out of range
}
}
} // touch
} // default

Thanks for that - it is a real help.

You might also want to test to see if the result of llGetObjectDetails() is an empty list. If so, the target avatar is offline or not present in the vicinity.

It's done in a certain way when I check if (pos != ZERO_VECTOR).

llList2Vector([], 0) == ZERO_VECTOR

No need to manipulate lists more than necessary.