This has been discussed here a few times before (search: horn lock). It seems the answer is no, it can't be turned off. The PM UC5 is missing that setting, plus some others. It doesn't seem the dealer can disable it either. Our VW just chirps quietly, but the PM horn is full blast. At least it doesn't honk when locked from the inside. There is also a theory that only PMs with factory security systems (ours) honk and flash, otherwise they only flash. Can anyone with a PM newer than RD's 2015 and no security system confirm theirs doesn't honk? It would be nice to know that before ordering the factory security system.