Aftermarket Alarm and retain key fob

I have purchased a used 2015 Prius which does not have an alarm only keyless entry. I would like to add an alarm system and trying to see my options before going to the dealership and purchase a factory alarm system.

I am looking for an aftermarket alarm that can integrate into my existing key fob. Would any have any recommendations. I've looked around but none of the brands show whether they can integrate or not.

Thank you.

 

I have techstream already. I enabled the security system, but upon testing nothing happened when I manually unlocked the door manually. I am guessing I don't have the security brain installed. Unless I am doing it wrong, can someone point me in the right direction.

I am not concerned about my car getting stolen, but more about someone breaking my glass or stealing my cat converter. And yes, cat converters are pretty popular here in LA.