Seems it is the visitor's phone scanning the QR code, which means whatever mechanism sends the text has all the identifiers of the phone which scanned the QR code, right? If it protects the visitors' numbers from disclosure, that's great, but there is no assurance (and none that could be given and absolutely trusted) that they are not disclosed.
OK, maybe the point is to not install any hardware (beyond a sticker), but it seems people are pointing out that a QR code introduces more problems than it solves (trust, spoofing, copying, misdirecting, inconvenience, etc.). If he wants to install no hardware and get a text on his phone, perhaps the easiest thing is to post a sticker with "pls text me at [mobile number]" at the location of the doorbell or QR code?
It would be possible to encode the phone number in the QR code and just send a text, but then you could just print out the phone number and write "text me" next to it.
Given that they have an app I'm sure the QR code leads to a link that will trigger the notification via app on the phone, no text message anywhere.
Again to your last point, no text message, dude just wants to get a notification on his phone without installing some dumbass $300 doorbell
OK, maybe the point is to not install any hardware (beyond a sticker), but it seems people are pointing out that a QR code introduces more problems than it solves (trust, spoofing, copying, misdirecting, inconvenience, etc.). If he wants to install no hardware and get a text on his phone, perhaps the easiest thing is to post a sticker with "pls text me at [mobile number]" at the location of the doorbell or QR code?