Horn beeps twice when unlocking

[Wingman]

Hi,

I have a 2001 model 2.7 Boxster. In the last few days the central locking seems to activate itself while I'm driving, when I try to switch it off, it comes straight back on and the car beeps twice . Also, when I switch the car off and open the door, the window on the drivers side does not lower. The strange thing is, when I activate the roof down lever (Apologies for not knowing the technical name), both windows lower. They also both raise when I put the roof back up.. The speed dial and mileage lights are also staying on, even when the key is out of the ignition.
I believe that this points to a sensor issue as I read in the manual and other threads on here that when the horn sounds twice, it means there is a security issue. Before I take it in to the garage I wanted to know if there was anything I can do myself.

Thanks in advance