Assuming they have a smart phone (Bluetooth,) I think you are able to add them by phone number.

Failure of a Check-in and/or Response agent to obtain City certification within ninety days of their affidavit submittal may result in the suspension of the management agency or owner manager business license and authorization for rental activities at the TPHR unit(s) they represent.In other words you are not allowed to live in another city and self-manage from your beautiful coast using smartphone with Airbnb app and have auto replies sent from SmartBNB - service all AirB&B hosts love.

For example (among others), even in this time where 55+% of emails are read on smart phones, CoStar completely prevents users from seeing for sale listings on a smart phone that they email via daily notifications that meet your criteria. 

I am looking to use this on a 15+ unit and want to be able to control each door from my smart phone.

We have smartphones Ipads etc.

More specifically, I use smartphones to recruit train and manage and pay my bird dogs.I have some propriatory mobile software that's in development.

@David Dachtera I can't seem to get it work could it be because I'm using a smartphone?

Most smart phones these days have high quality cameras or you could buy a camera. 

Is it one of the cameras that attach to a smart phone or the next "step up" to a stand alone unit?

This is an industry disruption just like motor vehicles, the internet and smart phones.