zafira alarm fault?

can anyone help? i have a 2003 zafira gsi and the alarm keeps going off, the led light is flashing as soon as i lock the car instead of staying on steady for 10 seconds so it is saying there is a fault it the system somewhere, i had the local garage put it on the computer but is saying no fault code, i'v checked the bonnet switch, door switchs, sensors in the interior light boot switch and its not any of them, by reading alot of the answers on here it maybe the power sounder but have not had any beeps when turning off the ignition, i don't wanna take it to vauxhall dealer and be ripped off as i want to sell the car, is there anyway of disconnecting alarm? thanks chris