I got a notice that some of my contacts are on AT&T. Therefore they may not be able to receive text alerts as AT&T will be downgrading SMS. It suggest I change them to push notifications.
Can I do this without involving them? Or do they need to authorize push notifications on their end or install the ADC app?
To receive push notifications the individual would need the Alarm.com app on their phone and they would need to enable push notifications within the app settings. Once enabled you would be able to select their phone as a recipient for any notifications.
Correct, to receive push notifications they would need to have the app on their device and enable push notifications for it.
AT&T recently dropped support for their email to SMS gateway which is why those notifications are no longer working, see the post below for details and some user suggestions on alternatives.
One might be the Mobile Text Alerts extension for Gmail which lets you forward notifications as a text message based on sender and/or keywords.