list lAlerts = [];
float fTimer = 5.0; //Sekunden
float fDistance = 80.0; //Meter
float fNearbyDistance = 25.0; //Meter
integer iSecondsToClear = 600; //Sekunden
string sAlert = " ist in Sensorreichweite gekommen."; //Textnachricht
default
{
    state_entry()
    {
        llSetTimerEvent(fTimer);
    }

    timer()
    {
        list lNewList = llGetAgentList(AGENT_LIST_REGION, []);
        list lAlertsTemp = [];
        integer iCount = 0;
        integer iLength = llGetListLength(lNewList);
        key kID;
        float fDist = 0.0;
        for (iCount = 0; iCount < iLength; iCount++)
        {
            kID = llList2Key(lNewList, iCount);
            fDist = llVecDist(llGetPos(), llList2Vector(llGetObjectDetails(kID, [OBJECT_POS]), 0));
            if (fDist < fDistance && fDist > fNearbyDistance)
            {
                if (llListFindList(lAlerts, [kID]) == -1)
                { //alert
                    llOwnerSay(llGetUsername(kID) + sAlert);
                    lAlertsTemp += [kID, llGetUnixTime()];
                }
            }
        }
        lAlerts += lAlertsTemp;
        lAlertsTemp = [];
        iLength = llGetListLength(lAlerts);
        for (iCount = 0; iCount < iLength; iCount = iCount + 2)
        {
            kID = llList2Key(lAlerts, iCount);
            if (llGetAgentSize(kID))
            {
                if (llGetUnixTime() - llList2Integer(lAlerts, iCount+1) < iSecondsToClear)
                { //Agent still in sim, and alert less than 10 minutes.
                    lAlertsTemp += [kID, llList2Integer(lAlerts, iCount+1)];
                }
            }
        }
        lAlerts = lAlertsTemp;
    }
}