Hi. previous post forgot to say my car is a 2013 Antara 2.2 CDTI 5 door. 

Said before alarm going off without any reason, have been told told clean sensors on bonnet and tailgate, but it could be the 

alarm sound horn but I don't know where it is located.  It has been sugested that it is located under the battery so sounds like a big job

to replace. Any ideas would be welcome.

The horn is under the battery tray and has its own battery connected to it. Good luck finding a replacement one, like everything with the antara, all the parts are like trying to find rocking horse poo. I wuld try disconnecting the tilt sensor under the passenger seat first and see if that fixes it, as passing cars ,trucks etc can set off the alarm by rocking the car and the tilt sensor if faulty will think its being moved.