On Phone Apps to Unlock Doors

Have had an interesting home modification enquiry – are there any phone apps that can be used to unlock a front or back door of a home?

I have found a product where a visitor can ring the door intercom and a push notification is sent to a phone. The phone rings and the person can answer the phone, see who is at the door and open the door using their phone. I like the idea that the phone user can see who is at the door

Other options described in last weekend’s Australian Financial Review for door lock access:

KISI door lock (e-keys are given to visitors)

KEVO by Kwikset (blue toothed powered lock that retains a lock for a mechanical key)

August Smart Lock (controlled by smart phone app)

Schlage Touchscreen Deadbolt (use of codes entered into its pad or via the internet)

Has anyone used the above or have any other ideas?