Do you have a recommendation for a siren to place in my attic? I have power and can wire directly to 2GIG panel.

A couple different forum discussions on this topic (The second discusses midway down):

We have seen a lot of praise for the Lowes Iris (Utilitech) Zwave siren partly due to its low price point, but you’ll need a couple Zwave repeating devices between it and the panel depending on distance from the panel, considering you want to put it in the attic.

If you want to go with a wired siren, choose one with a roughly 6-14 or 9-14 volt activation and max current draw of 120ma

Attics can get pretty hot. Make sure whatever siren you choose is able to handle the temperatures your attic reaches. Check the datasheet for the specs. A wired siren is probably going to be able to handle higher temperatures.