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Hi, it sounds like your alarm siren has gone bad and it may have blown the fuse. Check fuse #8 in the trunk fuse box and see if it is blown. If it is you can replace the fuse and get the remote working again but your siren may still go off randomly. You will probably need to replace the siren to repair the problem. It's also possible that the battery in the remote is not making good contact.
Let me know what you find out.
Click on the fuse box diagram below. It won't be a missing relay problem.