Revenine

Hello, I've recently been using Skoda Octavia II 1.8 TSI and I encountered weird problem. I dont really know if they are connected so bear with me please. Previous owner installed Cobra alarm in the car. Sometimes when I lock the car with the remote after some time it starts to emit three distinct sounds while flashing the emergency lights, its like the car alarm, but I think the alarm itself is like 10x much more noisy, so its seems like weird kind of signal, some fault maybe? The sounds sometimes appear 2-3 hours after locking and sometimes never, other times its repeating every 10-15 minutes which can be really annoying. The only think that seems to help is to open all the doors, close them and lock the car again. Moreover whenever I try to start the engine "service" is displaying on the led screen. I dont really know if its connected like I mentioned, but no other indicators are showing, so I dont really know what to look for. Before I drive to the mechanic and possibly lose ton of money for deleting errors. I would like to ask if anyone encountered such problem? The noise thing is really getting annoying, otherwise its literally the best car I drove in a long time. Regards, Revenine