well i fitted this alarm, they retail for about £20-25, so i wasnt expecting much tbh.
it is so easy to fit! just 2 wires, + and -
it goes off when the door or boot is opened
and it goes off when its hit with a ball, so would go off when a window is smashed, if you dont have an alarm because you cant afford one, i really recommend this! tbh, i dont think il be getting a better one as it does exactly what i want it to do 
it is so easy to fit! just 2 wires, + and -
it goes off when the door or boot is opened