If the alarm on your 2007 Honda Civic Ex is broken and continues to go off, you can disable it simply by removing the alarm fuse. Although this should not be a permanent solution, removing the fuse will allow you to take the Honda Civic to an exert in order to analyse the problem. The alarm fuse is located in the fuse block of the Civic, which is in the engine compartment. It should only take you a few minutes to remove the Civic's alarm fuse.
Pull the bonnet release lever of your Civic to open the bonnet.
Lift the bonnet and use a socket wrench to remove the Civic's negative battery terminal cable.
Lift off the cover of the Civic's fuse block.
Use a fuse puller tool to remove the fuse in Slot 7. Note that this will also disable the horn, so make sure this is only a temporary fix.
To enable the horn again, simply install a 15A fuse into Slot 7.