2003 Accord Passive Lock?

Hey all,

I bought a used 2003 Honda Accord EX w/ a factory alarm. The alarm does most of what I need [keyless entry, alarm, etc.] but I would like to have passive locking as I sometimes forget to lock the doors. My last accord had an aftermarket [?] model that did this.

I have heard rumor of a alarm remote button combination that can enable passive locking on the factory system; can anyone confirm this? Or can someone recomend something that I can install to allow passive locking?

Thanks,

Bruce
Atlanta, GA