For automated messaging I use this service https://superhosttools.com/ It lets me send automatic messages when a person books, check-in instructions at a specific time I am able to define before check-in, parking instructions shortly before they arrive, a message checking in on them the next day if its a multi-day booking, and a checkout day message. It also automatically leaves my guests a 5-star review a couple days after their stay and asks them to rate me back -- unless I rate them manually before hand. Has a timeline view letting me see what messages will be sent in the future which I can cancel or change as needed.

For cameras at all my rentals I bought these Dericam ones https://www.amazon.com/Dericam-Security-Surveillance-Weatherproof-Pre-installed/dp/B07Q39PJZW I like these over the Amazon Ring cameras as there is no additional monthly fee and they follow standards like RSTP. The apps they come with are pretty decent but the openness of the camera let me program my own customizations. I'm a programmer by trade so I do a bit of my own programming of all my devices and services to tie it together in a nice cohesive system.

At the heart of a lot of automation I use raspberry pi's with software called home assistant from https://www.home-assistant.io/hassio/ Again I chose this over other commercial smart home hubs because of its openness and ability to customize with a bit of programming. The system can control my thermostats, locks, and a few lights.

At one of my rentals I have a Kwikset Z-Wave keypad lock. With a bit of programming I have the home-assistant software automatically set the key code of the lock to the last 4 digits of the guests phone number. It reads it directly off my airbnb ical calendar. The automated messages sent to the guest simply tell them to enter the last 4 of their phone number they have on file with airbnb. I never have an issue with this lock. I do have a backup lock box here, but I never told guests about it. My backup lockboxes are these mechanical low-tech devices https://www.amazon.com/gp/product/B073VZ72PW

My other 2 rentals, including the one with the issue with these bad guests have a different smart lock that are mostly self-built. Both of these rentals already had a 40+ year old buzzer lock on the front doors. I wired in a relay switch to these buzzer locks and connected it to the raspberry pi devices controlled by the home assistant software. I setup a simple web server that can unlock the door with a special URL that contains the guests reservation ID. It only allows door access between the guests check-in and check-out time. My automated check-in messages send guests a message with a URL to the door that contains the reservation id. It's clickable within their airbnb app and opens the door for them. Most my guests love it, but I would say 1 out of 4 guests don't. Some just aren't comfortable with a smart phone enough to operate the door. So the backup lockboxes at these rentals get used a lot more that I just started sending every guests the code the the lockbox. My mistake for sending it too early. The Z-Wave keypad lock on my 3rd rental seems easier for guests and for me to manage, I may just end up getting those locks at my other rentals too.