When people arrive all at once on the parking lot across the street, they lock their vehicles almost simultaneously. The result is "Beep! Beep! BEEEP!" And the slightly more subtle but no less invasive whistle or chirp.
For the vehicle owner holding the key, there's nothing upsetting about it because they're controlling the noise. They know it's going to happen. But for someone nearby who isn't expecting it, it can be an unpleasant shock.
Someone recently told me she actually gets a kick out of seeing people jump when she blow/locks her vehicle. How perverse is that?
Blow-lock...hmm. We need a new word for it: Bloke?
Some horns are very loud. Say a polite word to the owner and for your trouble you get a blank look and denial: "I didn't blow my horn!" Press the point and you get the offended response, "I'm not blowing my horn, I'm locking my car!"
The law against unnecessary horn blowing still exists, folks. Horns should be used only for emergency situations. When we hear them all the time, we may be startled for a few moments but often don't even turn to look any more. It's numbing, and it's unhealthy. Search "noise health" and read more about it.
Cars have been around for more than a century, and for most of that time we've been able to lock them just fine without making a sound. Sometimes new technology is a giant leap backward.
Oh well, it could be worse -- imagine if someone invented a system that blew the horn every time you stepped on the gas!