Ok, so it’s illegal IF it’s a nuisance. I can assure you I won’t be sat just locking and unlocking the car for sh*ts n giggles. You also said it’s very quiet and therefore doesn’t fit in to that category as I presume it will be under the required dB level. Additionally, I’m a 9-5 worker and wouldn’t be locking/unlocking at unsociable hours. IF it was loud enough to wake the neighbours I’m confident they would rather be aware of someone stealing keys in the area.Fits into the noise nuisance category it's illegal to sound a horn if stationary without good reason, highway code. Locking the car isn't one.
It's American and Far East cars which have the beep enabled traditionally. You find it on rental cars out there. Disabled in Europe. It may be the chirp VAG has fits into the legal audible limit but either way it's considered poor form in Europe which is why it's coded off, but the coding left there for outside Europe.
It’s not the horn that sounds so doesn’t fit in to that category of the Highway Code either (you also mentioned that it wasn’t the horn).
I apologise for the poor form that you clearly don’t agree with but let’s keep this thread on topic and supply coding rather than opinions