Trigger not working for Text Items.

I have installed and configured Zabbix 1.6.2 on a Centos 5 .
I have installed and configured SNMPTT and the snmptrapd daemon
Traps successfully arrive at Zabbix.

Below you can see the command i use to send the traps with Snmptt.conf
EXEC /usr/local/sbin/zabbix_sender -v -z localhost -p 10051 -s $r -k snmptraps -o "$aA::$s:: $N - $Fz"

Also the arrived trap from the history in zabbix look like this:

x.x.x.x::OK:: Alarm_OFF - Video running for x.x.x.x
x.x.x.x::Critical:: Alarm_ON - Video stopped for x.x.x.x

were x.x.x.x is ip address.

What I need to do . I need to have a trigger that comes on when Alarm_ON and go off when Alarm_OFF . Also when I receive anything else I need zabbix to ignore it .

Finally I need to have this triggers to Auto-close themselves.

For example Alarm_ON and the status in Zabbix = problem
Alarm_OFF and the status in Zabbix = OK

I have tested items both with text or character configuration but is it seems that the command

{x.x.x.x:snmptraps.str(Alarm_ON)}

=1 for example doesn't work.

Just to mentions that I am using /usr/local/sbin/zabbix_sender and not the sh or perl script .