Horn mysteriously starts blowing while sitting in my driveway. Even if unlocked and alarm is not engaged.

the remote key would be the easiest (and cheapest) thing to try first but i don't think that a low battery in the fob would activate the alarm randomly , i'd get the OBD codes read as will point to which part of the anti theft/central locking system is causing the issue

Make sure horn unit is grounded properly

This may be stupid but have you locked and unlocked the
drivers door (with the key,not the remote)?

try checking the fuses

Could be a short in the wire to the horn. I would inspect it under the hood. The horn has power even when the key is off, so a short could cause this. If it`s in the steering wheel, I would let a professional work on it, since working around the airbag sensors is dangerous.

there is a short in the horn wiring, you may disconnect the horn relay, that the easiet thing to do. owners manual should have a layout of where the relay is. Steering wheel switches most likely.

you can disconnect the horn by pulling the airbag out of the steering wheel and simply disconnecting the horn wire. be sure to disconnect battery before you touch the inflatable restraint. it may require special tools to remove air bag.

All VW's have electrical problems sounds like a relay switch isn't working properly or you have a serious eletrical problem. And if's a 1.8 turbo boy are you in for a headach. That cars a nightmare I know cause I've worked on these cars and VW won't recall any of them. Best thing to do is try to fix it and dump it.

do you have a alarm on it. If so you need to disable it or turn it off. Other wise you have a short somewhere in your horn. disconnect the horn under the hood. Its usually upfront and looks llike a flat black circular device that has one wire going to it, unless you have a alarm then it may have more.

tepfy