Who to know which sensor is faulty in alarm system?

[wawa]

Hello

When I lock the car with the remote key, I got a small beep from the horn, meening something is not close correctly. But every thing is well close. So I guess I have a sensor trouble. Is there a way to know which sensor is faulty or not sending signal to the alarm system? A code I can read somewhere or do I need to have the car connected to a cumputer to find out where is the trouble.

I would like to correct that small problem.

thanks
wawa